Here to return to
SALT MARSHES — THEIR PAST AND FUTURE
IN a study of the past it is convenient to have some definite point from which to date. To the original settlers on these shores Noah’s flood was a very real catastrophe, in which everything on the earth was washed clean, and, by a reference to the Bibles of those days, or even to the Bibles of fifty years ago, one may learn that this flood occurred 2,349 years before Christ. To our forefathers the time that had elapsed since the flood was a long period to contemplate, but nowadays we are contented to look upon the fifty thousand years more or less, since the last glacier left these shores, as a mere moment of time in the great past. There is no doubt that the glaciers compared favorably with Noah’s flood in cleansing power. Everything of an animal and vegetable nature has come in since then, including the salt marshes themselves, which are made up of various growing grasses on top, and, in their entire thickness of closely woven sod and thick black soil, they are largely of vegetable origin. One must picture this region at the close of the glacial period, therefore, as entirely destitute of the most striking feature of to-day, a region of brown land and blue water, but lacking the great blanket of green marsh.
As one looks inland from the Ipswich dunes over the broad plain of salt marshes, the rounded form of Hog Island — the birthplace of Rufus Choate — looms up as a conspicuous object in the landscape. It is a typical drumlin, one whose duplicates are to be found everywhere in northern Europe and America, where the ice sheet of the last glacial period formerly held sway. It is a smoothly rounded accumulation of turf-covered gravel a hundred and forty feet high, somewhat steeper on the north than on the south side, but as featureless as an inverted punch-bowl. On the western side its curves are cut by the flat plane of the salt marsh. Scattered here and there in the marsh are to be seen lower rounded or oval islands, some of them covered with trees, while in the Castle Neck River is a small circular gravel island so low that it is all but overtopped at high tide.
Aside from the thin coating of soil and vegetation, Hog Island shows scarcely any evidence of change by wind, water or frost that have been acting on it since it emerged from the glacier’s bed. We are indeed very close to the glacial period, and the interest in arctic life and adventure, an interest which is common among northern people, and extends even to the delicate of both sexes, is, perhaps, an inheritance from the times when glaciers spread far down among the homes of our ancestors.
Shaler in writing from Florida said: “The nearer I get to the tropics the more I turn with pleasure to our grim northern clime.”
It is well that this love of the ice, which is often incomprehensible to those of southern ancestry, continues to exist, for who can say but that the glaciers of Greenland and Alaska and Spitzbergen, of the Alps and the Himalayas may not again wax and spread over regions now in the temperate zone? May it not be that the present is merely one of the interglacial periods which have occurred again and again during the ice age? Indeed, there is reason to believe that some of the interglacial periods of the past were even longer than the interval of time which has elapsed since the ice receded.
In order to picture the land as exposed by the receding glacier, we must not only strip off the salt marsh, as well as all other evidences of vegetable and animal life, but we must do more than this, for, as we shall see, there is every evidence of a former higher elevation of the land in relation to the water. There are also reasons for believing that as the land sinks, the marsh, soft and uncertain as it seems, is really more stable than the everlasting hills, and maintains itself at the same point.
Some of the low oak islands in the marsh are doubtless the tops of drumlins or of smaller glacial hillocks, as is shown by their circular or oval outlines and gravelly formation, while the round pebbly island in the Castle Neck River is of the same nature, but is now so nearly submerged, that all humus and land vegetation, as well as the finer particles of the top of the gravel hill, have been washed away in stormy tides, and nothing but boulders and sand is left.
If the land had remained at the same level as it was at the close of the glacial period, we should be able to discover some traces of ancient shore line where the sea waves formerly pounded, some old beaches with sub-fossil shells and crabs on and under the borders of the marshes, separated now from the sea by acres of green salt turf and by barrier sand dunes, which, like the marshes, are of recent formation. If on the other hand the land had risen at various rates, we should find a series of flat terraces or several elevated beaches, as on the Labrador coast to-day, where one sees two or even three beaches one above the other, some of them two hundred feet or more above the present sea level and almost as clean as when the surf beat on them. In this Ipswich region, however, there are no traces of old terraces or beaches, either at high tide level or above. Hence the land could not have been stationary or rising. One alternative alone remains, namely that the land has been slowly sinking, a process in which all landmarks are covered up or “drowned.” Of course the same results would obtain if, instead of the sinking of the land, there had been a rising of the water, and the theory is held by some that the amount of water in the ocean was tremendously increased by the melting of the glaciers during their recession. It hardly seems possible that this would account for the difference in level which seems to have taken place during the last thousand years or so, at the same time that an opposite change has been taking place in Labrador. Be that as it may, if one stands at the top of Hog Island at high tide at the full of the moon, and looks out over the waste of waters extending several miles inland, flooding all the marshy valleys and making veritable islands of the drum- lins, one is impressed with the force and accuracy of this term drowned.
THE MARSHES AND HOG ISLAND, HIGH TIDE
At a number of places along the coast of Essex County the evidence of the changing level of the land is shown so plainly that he who runs or even swims may read, for there are stumps of forest trees still in position in leaf-mould and peat beds below the level of high water. In a cove near Bass Point at Nahant the stumps of white pine and white cedar, hemlock, spruces, ash, oak and maple are to be seen covered by thirteen to sixteen feet of water at high tide. In Lynn Harbor, and in the Saugus marshes, at Swampscott, Marblehead, Manchester and in Salem Harbor, these remains of submerged forests are also found, while near Misery Island, when the tide is low and the water still, stumps of forest trees may be seen at a depth of twelve to fourteen feet. In a marsh at Ipswich that is flooded by the great tides of the full moon of spring and fall, several stumps of great trees are to be seen imbedded in the salty peat. One of the old farmers told me that when he was a boy an old man used to say that his father remembered when this region, now filled by the black-grass marsh, was occupied by a grove of forest trees. Professor E. C. Jeffrey very kindly examined chips from two of these stumps for me, and found that one was a white pine, and the other a swamp white oak.
In 1804 and 1805 Dr. Nathaniel Bowditch prepared a chart of Salem and Marblehead harbors, giving the soundings over various ledges and rocks. Ninety years later, in 1894, careful measurements were again made at these same points and under similar conditions of tide and moon, by the late Professor John H. Sears. In all cases the water was found to be from one to two feet deeper than it was ninety years before. In 1903 Mr. John R. Freeman concluded that the land in Boston and vicinity was sinking at the rate of a foot in a hundred years by comparison with various ancient and modern tide gauges; also by the fact that the sills and floors of the masonry dry dock at the Charlestown Navy Yard then stood about nine inches lower relatively to mean sea level than they did seventy years before, while the dock stood at precisely the same level relatively to points on solid ground.
An incontestable evidence of a former higher land level is presented by the deep channels of all our eastern rivers, up which the tide rushes for many miles, and by the fact that these channels extend for a long distance out to seaward under the water. Only when the land stood at a much higher level could these channels have been cut.
Another strong evidence of subsidence is shown in a study of the sections of the marshes, for, as we have seen, the various species of grasses are limited to certain zones in relation to the tides. As remains of grasses are found in the sod sections several feet below the level at which they can now grow, the inference is plain that portions of the marsh formerly stood higher in relation to the tides. Professor Charles A. Davis has made a careful study of the marshes about Boston by means of borings, and he has found even at a depth of twelve feet below the surface of the marsh, peat that was composed of the grasses now growing on the surface.
It must be remembered, however, that the height of the tides is dependent very much on the character of the shore line, as Professor D. W. Johnson has shown, and as this changes from time to time independently of changes of land level, regions not previously flooded may suddenly be drowned by high tides. This fictitious appearance of coastal subsidence, however, need not blind our eyes to the many incontestable evidences of true subsidence which cannot be so explained.
As an example of the possibility of erroneous interpretation of marsh deposits, the case of a similar seashore region, that of the North River valley at Scituate is instructive. Here for many years prior to 1898 the mouth of the river bed had been so silted up that the tides were practically excluded — and the level of the marsh, which supported a fresh water vegetation, came to be, as subsidence continued, several feet below the level of high tide on the outer beach. In the great November storm of 1898 the sea broke through the barrier beach some distance from the mouth of the river, and since then the tide has ebbed and flowed freely in the valley, drowning out the fresh water vegetation and killing grass, bushes and trees. The marsh of a salt water formation is gradually building up to the high tide level. Suppose, then, that in the course of centuries this new mouth should become silted up, the influx of salt water excluded as before, the marsh would again take on a fresh water character. If these changes were repeated several times a section would show alternations of fresh and salt water deposits. The unwary geologist might infer, and his inference would be extremely plausible, that there had been times of alternate elevation and subsidence of the land, whereas in reality there had been all the time a subsidence.
The evidence of the sinking of the land seems to me plain, but why is not the salt marsh drowned too, or rather why is there any salt marsh formed at all? As the land sinks and the water rises it would be easy to picture the gradual extension of the sea into the land, the waves lapping the shore, all the time reaching higher and higher, until even the old glacial hills were overflowed. This would certainly be the condition of things if the marsh did not build up as fast as the land sank, and the upbuilding can be seen in all the zones of the marsh.
Everywhere in the creeks and estuaries, shut out by the sand dunes from the impact of the waves of the sea, forests of waving eel-grass flourish and entangle the fine sediments in their meshes, and help build up this zone. When the sand brought in by the tides and storms has accumulated in shallows so that these flats are sufficiently exposed at low water, the thatch grass claims it, and entraps the finest mud among its stalks. Into this the grass from its hollow stems sends out higher and higher roots, and the whole becomes compacted into a loose sod of mud, stems and roots, a soft, muddy, peaty mass. Thus, though the very foundation of things is sinking, the bottom does not drop out, and the depression is so gradual that the grass easily keeps pace with it.
THATCH GRASS BUILDING OUT ON THE EDDY SIDE OF A CREEK
THE BANK FALLING AWAY ON THE CHANNEL SIDE OF A CREEK
As the tide sweeps alternately up and down the estuaries twice a day each way, it bounds back and forth from side to side with great symmetry of rhythm, eating away one bank by its swift current, while the opposite bank extends itself outward in comparatively calm water or in counter eddies, and here it is that the thatch grass flourishes. Another place where one can watch the extension of the thatch, the pioneer in this great march of the marshes, so to speak, is on the large sand flats gradually building up in regions of comparative calm outside of the full swing of the tides. On one such flat in the Castle. Neck River there are now nine thatch islands from two to twenty-five feet long, besides five small single tufts of grass, and none were to be seen there twenty years ago. In another place a large thatch island a hundred yards long and half as wide has appeared and grown within the memory of one of my farmer neighbors in the last sixty years. A shift in the currents may in a short time wash away this work of years, and may even enlarge some of the creeks, but I am inclined to think that the general tendency is toward a contraction of the tidal estuaries by the enterprising thatch.
The third zone, that of the marsh hay, which constitutes the greater part of the broad marsh, is in the same way able to keep its level in relation to the water by the gradual deposition during high tides of fine mud and sand, and by the climbing up of the grass on the shoulders of its dead ancestors. In the swirl of the tides the sand and mud are constantly carried up from the sea, and while the sand holds its place in tolerably swift water, the mud comes to rest only in regions of comparative calm. Both are dropped in periods of quiet water between tides. The fresh water detritus brought down by the rivers here is so small in amount that it plays but an insignificant part in the building up of the marshes.
In calm weather a surprising amount of sand is borne along by the rising tide, floating on the surface in the same way that a needle can be floated in a tumbler of water. The slightest touch of a grass blade or a cat’s paw of wind sends the sand to the bottom. In winter, ice cakes, with mud and sand frozen into their lower surfaces, or bearing loads broken away from the banks, are often stranded far afield by the high winter tides, and, in melting, materially help in the building up of the marsh. A certain amount of sand is blown inland over the marshes from the dunes.
ISLANDS OF THATCH AT LOW TIDE
MARSH AND CREEK AT HIGH TIDE
The fourth zone of vegetation, the zone of the black grass, which fringes the whole region, is visited only by the exceptionally high tides, and very, very slowly creeps up on the fresh water land, displacing the life there, be it fragile herbs or mighty forest trees. All yield before the strength of the salt sea. It has been found that one and a half per cent. of common salt in the soil is poisonous to plants that do not naturally grow on the seashore, while sea water contains two and a half per cent., and the soil of salt marshes, on which all these halophytes, or salt-loving plants, grow, may contain even more salt.
In other words, the vegetation of all the zones holds its own, and in places more than holds its own against the advancing sea. A slight increase in the rate of subsidence might reverse this, and the sea would drown the grass, and great inland bays of sea water would replace the marshes. With a cessation in subsidence, the estuaries would become more contracted, and the fresh water vegetation would very gradually creep down upon the marsh. A change to a movement of elevation and the salt marshes would in the course of time cease to exist.
Accurate maps of the marshes made from time to time, even in the brief space of the white man’s occupancy, — less than three centuries, — would be of great value in showing the changes that have taken place, but such maps are lacking. In England, however, history goes farther back, and there is plenty of evidence that the marsh lands of East Anglia, the region of the Norfolk Broads, which corresponds in many ways with this Ipswich region, have become less and less invaded by the sea, notwithstanding the subsidence which is going on there as here.
When the Romans devastated the country, they sailed far up the great tidal estuaries, which are now narrow sluggish streams meandering through meadows of fresh grass, and attacked the ancient Britons in the highlands at Reedham and Norwich, now eighteen miles from the sea, and here they “buylded toures on the dynes of the ocean in dyverse places.” One may read in the Saxon Chronicle that in the year 1004, Sweyn with thirty ships plundered and burned Norwich. Even as late as 1327 it is stated that Norwich is “situate on the bank of a water and arm of the sea, upon which ships, boats and other vessels have immemorially come to their market.”
Accumulations of silt and the growth of vegetation, narrowing these estuaries into sluggish streams, with here and there dwindling sheets of shallow water called broads, can be explained by the cutting off of the sea and tidal currents owing to the formation of sand-bars and later of dunes at the mouths of the rivers. The most famous of these sandbars is the one on which the fishing town of Great Yarmouth now stands. Even before the Norman Conquest the sand-bar at this point had become a sand bank frequented by fishermen. Later man cooperated with the ocean by building dykes and drains and erecting wind and steam pump-mills still more to exclude the salt water, and hasten the deposition of mud and sand and the building up of vegetation.
That subsidence is still going on, however, is evident from the fact that parts of the Broadlands are below the level of high tides, protected from the ocean by only a narrow strip of sand dunes. In places the sea is gradually gaining on the sand, so that the ruined church of Eccles, found by Lyell half buried in the dunes in 1839, has since been entirely destroyed by the waves, and it is feared that the sea will finally conquer and flood the sunken land.
From these same Norfolk marshes nearly three hundred years ago came to the Essex marshes in the new world many of the ancestors of the present inhabitants. It is pleasant to fancy that the love possessed by some of us for salt marshes may be inherited from our English forebears, who long years ago hunted and fished in the marshes and tidal estuaries of old Norfolk.
One can see in the mind’s eye the recession of the glaciers, the bare gravelly hills and the numerous streams coursing over the sandy boulder-strewn plains high above the sea, which was then many miles to the eastward; the coming of plant and animal life, including that of man himself; the cutting down of the streams, the slow gain of the sea on the land as the latter sank, and its extension in the form of estuaries into the river valleys; the piling up of the barrier sand reefs and later of the dunes, and the extension and building up of the salt marshes, keeping pace with this depression, and their gradual march to the westward as the sea gained on the land.
Shaler said of the salt marshes: “The remote and picturesque coral reefs have long proved fascinating subjects to the geological student, while these near-at-home structures, which are in their way almost as interesting as the work of the polyps, have never been adequately studied.”
Those who decry the study of science as dry, and advocate the reading of fairy stories and romances only for the cultivation of the imagination, are evidently totally unaware of the pleasures and possibilities of geology.
The question is often asked whether these marsh drumlins, now covered only with grass sod, were ever forested, and we are fortunate in possessing an early description of this region by Captain John Smith, who landed at Agawam, the Indian name for Ipswich, in the year 1614. He says: “This place might content a right curious judgment; but there are many sands at the entrance of the Harbour, and the worst is, it is imbayed too fayre from the deepe sea. Here are many rising hills, and on their tops and descents are many corne fields, and delightfull groves. On the East is an Isle of two or three leagues in length; the one half plain Marish ground, fit for pasture, or salt ponds, with many faire high groves of mulberry trees and gardens. There is also Okes, Pines, Walnuts and other wood to make this place an excellant habitation, being a good and safe harbour.” The Indians were in the habit of clearing the ground by burning, and to this is due the openings for their corn-fields and gardens.
It was indeed a favored region, a happy hunting ground, and the Indians lived here in comparative peace and plenty before the white man came with his devastating diseases, his fire-water and fire-arms, and his corrupting morals. On the drumlins and in the dunes are many evidences of the departed race, — ancient shell heaps of clams and oysters, — for oysters formerly throve here, and, intermingled with them, bones of the great auk, of ducks and waders and turkeys, of deer and bears and seals. Arrow-heads, sinkers, stone axes and skin scrapers, and bits of rude pottery are still to be found in the shell heaps and in the fields round about.
A MARSH ISLAND
THE OLD CANAL.
Another record pointing to the forested condition of the drumlins is an ancient law passed in 1650, whereby the felling of timber on Jeffrey’s Neck, Castle Neck and Hog Island was prohibited, although we learn that in 1670 all fishermen were allowed to cut wood there for house building and fuel. In 1726 a deed of sale was executed for “wood that now is, or that shall hereafter be standing, lying or growing on any part of Castle Neck so called beyond Wigwam Hill.”
Although the larger drumlins, like Hog Island and Jeffrey’s Neck, are now nearly bare, except for the willow trees planted to shelter cattle, the smaller islands are covered with trees and bushes and are spots of much interest to the botanist. Red oaks are the common trees, but white birches, poplars and hickories also occur, as well as a few swamp white oaks, canoe birches, sassafras and lindens, and on one island a few red pines and on another a grove of white and pitch pines. Dog’s-tooth violets, oak-leaf gerardias, hepaticas and feverwort are also to be found on these islands. Oak Island in the Lynn marshes has been studied for years, and nearly four hundred different kinds of plants have been found there. It would seem as if the plants had gathered from all sides to avoid the rising tide of the salt marsh!
The meadows but lately reclaimed by the slow process of nature from lakes and ponds, the recently formed salt marshes and the sand dunes last thrown up by the sea, were then as now destitute of forests. One can easily discover by a simple experiment that in as short a time as ten years a sod-covered upland will return to an incipient forested condition, provided three destroyers — fire, the cutting tools of man, and the teeth of browsing cattle are excluded. Wild roses and blackberry brambles first spring up in the grass, and bayberries, hardhack and barberries soon follow. The more cover these give for the birds to nest and roost in, the more seeds are dropped there by these natural forest planters, and sumachs, thorns, rum cherries, apples, maples and red cedars soon appear.
So much for the marsh and its prominent features, and so much for its past history. How about its future? As Hog Island is a hundred and forty feet high, one can easily calculate that if subsidence continues to take place at the rate of a foot a century, and if the sand dunes continue to pile up and shut out the sea, so that the marsh may build up at the same rate, it will take fourteen thousand years before Hog Island disappears below the mantle of green marsh, which at the present time has almost surpassed the pebbly island of the Castle Neck River.1 What manner of man will there be to see, and echo answers what indeed?
Fourteen million years from now, the marsh, after long and deep burial under heavy loads of sediment and possibly of glacial till and of lava floods, may perchance be lifted up and emerge to the light of day from an eroded mountain side as a sandy coal-seam. Imagination refuses even to consider the condition of the human race at this remote period!
1 It is probable that if the coast continues to sink the barrier dunes Will move inland, so that instead of Hog Island being overwhelmed by the marsh it Will be battered by the sea in the same Way that Great Boar’s Head is now battered, and that it Will finally succumb to the assaults.