Popular Science Monthly/Volume 68/May 1906/Watkins Glen and Other Gorges of the Finger Lake Region of Central New York
Fig. 3. Cayuga Lake, one of the Finger Lakes, from the Cornell University Campus
|WATKINS GLEN AND OTHER GORGES OF THE FINGER LAKE REGION OF CENTRAL NEW YORK|
By Professor RALPH S. TARR
FOR some years there has been an effort made to induce the legislature of the state of New York to set aside Watkins Glen as a state reserve for the benefit of the public. As one of the most beautiful and most widely known bits of natural scenery in the state, it seems
Fig. 1. Sketch Map of the Southern Ends of the Cayuga and Seneca Valleys, Showing the Location of some of the Gorges.
Fig. 2. Photograph of Model of Ithaca Sheet. (By William Stranahan.
Fig. 4. Cross section of Seneca Lake, three miles north of Watkins. (Horizontal scale 1⁄2 inch to the mile; vertical scale, 1⁄2 inch to 1000 feet. Column of figures gives elevations in feet with reference to sea-level.)
Fig. 5. Cross section of Lake Cayuga Valley, two miles north of Ithaca. (Scale same as Fig. 4.)
longer present. To state this explanation calls for a preliminary consideration of the general topography.
The Finger Lake valleys extend nearly north and south, long and narrow, like so many fingers, the two longest, Cayuga and Seneca, being about forty miles in length, and at the lake surface from one to three miles in width. Their bottoms are below sea-level. They are excavated in the plateau of southern New York, a dissected plateau of nearly horizontal Devonian shales and sandstones, trenched by many deep valleys (Fig. 2). But among these valleys those of the Finger Lakes stand out prominently because of certain notable peculiarities.
If one of the upland valleys of the plateau should be damned so as to contain a lake as deep as Cayuga (435 feet) or Seneca Lake (618 feet), or even one a hundred feet in depth, its shore-line would be very irregular, and its waters would extend as bays up the tributary valleys. But in the Finger Lakes this is not the case. The lake shores are smooth and regular (Fig. 3), and this condition extends for several hundred feet above the lake level. The valley walls enclosing the lakes are gullied only by the narrow gorges which are so abundant (Fig. 1). Not only are they smooth and regular, but they are steepened below the 900-foot contour line (Figs. 2 and 3), so that a profile of the valley slope shows a distinct increase in the steepness of the valley wall below that level (Figs. 4 and 5).At the upper level of the steepened slope, upland valleys open out and lead back into the plateau, so that if the lake waters could be raised 500 feet higher than the present, they would enter into these tributary valleys and the lake shore line would become very irregular, as is natural in a stream valley dammed so as to hold a lake. These upland tributary valleys are broad and mature, having evidently required a long period for their formation; and their counterpart appears throughout the plateau region. They are the normal valleys of the region: the Finger Lake valleys the abnormal.
A significant view of these tributary valleys is obtained from the opposite main valley slope at such an elevation as to permit a view into them. Such a view shows that the broad valleys extend back into the upland, receiving numerous tributaries at the proper grade, and that these valleys are commonly enclosed between moderately sloping walls which flare apart as the lake valley is approached; but all this ends at about the 900-foot level, and the open mouth of the tributary valley is left hanging high above the main valley bottom on the edge of the smooth, steepened slope of the main valley. There the stream leaves its broad upland valley and plunges down the steepened main valley slope, into which it has sunk itself in a narrow and relatively shallow gorge, through which it leaps in a series of cascades and waterfalls.
Normally a tributary stream joins its main stream at an accordant grade, even in such a case as the Colorado River, where the main stream is rapidly deepening its valley. So general is this condition that a stream is ordinarily supposed to decrease in grade from head-waters to mouth at a fairly regular rate; and most streams follow this law. But here there is a normal decrease in grade up to a certain level, then an abrupt increase. Glen Creek, for example, which has formed Watkins Glen, descends at the rate of about a hundred feet to the mile for four miles, then falls in a succession of cascades four hundred feet in a single mile (Fig. 7). This change in grade accompanies a change from a broad, upper valley, over its lip into a narrow gorge cut in the smooth, steepened slope of the lake valley; and the same change occurs in the other streams of the southern half of Seneca and Cayuga valleys (Figs. 1, 2 and 6).
While the condition of smoothed, steepened main valley slopes and associated hanging tributary valleys is abnormal, it is not uncommon. It occurs in the fiords of Norway, New Zealand and Alaska; in the valleys of the Alps, Rockies and Sierra Nevada; and associated with it is a condition of gorges and falls below the lips of the hanging valleys. It is a notable fact that these regions, like that of the Finger Lakes, are regions formerly occupied by powerful glaciers; and it is even more noteworthy that hanging valleys and associated steepened, straightened main valley walls are practically absent in regions not formerly occupied by glaciers. So general is this association; so like the work of ice erosion, as we conceive it, is the anomalous valley form; and so unlike is it to the valleys of stream erosion origin, that physiographers are now quite generally agreed that the hanging valley and the broadened and straightened main valley are the result of glacial erosion.
There are still some who question this conclusion, but none of them has offered a satisfactory substitute or advanced a vital objection to the ice erosion explanation. It is a relatively new point in interpretation of land sculpturing and naturally is not universally accepted at the start. The same was true when the origin of ordinary valleys by stream erosion was proposed in place of the current explanation of catastrophes. In fact, some of the most ardent supporters of the ice-erosion theory are recent converts to it.
When the hanging valleys of the Finger Lake region were first recognized, and ice erosion proposed in explanation of them and of the main lake valleys, there were few who accepted the conclusions advanced; but now the great majority of American physiographers accept the ice erosion explanation for this region, as well as for others. The literature of glacial erosion is now extensive, and the fact of profound ice erosion in valleys freely followed by glaciers seems established; but it would be aside from the purpose of this paper to state the full argument for glacial erosion, Which, in fact, others have already done. Suffice it to say that glacial erosion will explain the conditions in the Finger Lake valleys, and no other theory so far proposed will do so. Moreover, these valleys were a highway for glacial motion, as is proved by the presence of pronounced moraines along their sides and at their heads.
When the glacial erosion theory was first applied to these valleys it was supposed that the erosion was simple and of a single period; but the discovery of other facts led first to a question whether some other explanation than ice erosion might not be necessary, and later to the conclusion that the phenomena are the result of a double period of ice erosion.
Of these facts the most important was the discovery of a series of buried gorges on the steepened slope in close association with the postglacial gorges or glens. In some cases the present stream has reoccupied these older gorges; in others it crosses them or follows them for only short distances. They are both broader and deeper than the postglacial gorges, and therefore required a longer period for their formation than has elapsed since the last ice recession. Being occupied by drift deposits of the last, or Wisconsin, ice advance, these gorges were evidently formed before the oncoming of this ice invasion. At first it was uncertain whether these gorges were of interglacial or preglacial age, though the former was strongly suspected.
A definite step toward the solution of the problem was made when it was discovered that in the Seneca Lake valley these older gorges do not extend below lake level. This is proved with especial definiteness on the western side of the Seneca valley, where for many miles there is a continuous rock outcrop along the shore just above lake level, and extending continuously across areas down which the older gorges must have passed. Watkins Glen illustrates this. The older, buried gorge leaves the Glen Creek valley just above the head of the postglacial glen a hundred yards or more above the point where the bridge of the Pennsylvania Division of the New York Central Railroad crosses the glen. It passes under the railway station and down the steepened main-valley slope under the sanitarium, its position there being indicated by a moderate sag in the hillslope, and, still better, by well borings at the sanitarium. Two wells, one at the sanitarium, the other a short distance west of it, fail to reach rock at 105 and 175 feet, respectively; but to both the north and the south of these wells rock is reached at depths of ten to twenty feet, proving the presence of a buried gorge. Below the sanitarium, along the line of this buried gorge, continuous rock outcrops occur, proving that the gorge is not continued there.
These facts prove that the buried gorges are also hanging, at Watkins fully 1,100 feet above the rock floor of the main valley. The interpretation placed upon these facts is as follows: Before the glacial period there was a system of mature drainage, with main valleys along the axes of Seneca and Cayuga Lakes, and with tributaries entering them at grade at the level of the mouths of the hanging valleys, that is, at elevations of about 900 feet above present sea-level. The advent of the continental glacier buried this land beneath ice, which moved with especial freedom through the north-south valleys, scouring them and leaving them both broader and deeper. The amount of deepening by this ice invasion was at least five hundred feet, and probably much more, the exact amount being impossible of determination at present, since much of the evidence was erased by later ice erosion. Moreover, the first ice advance may have left lakes in the valleys, whose surfaces acted as temporary base-levels, below which the interglacial gorges could not be cut.
With the recession of this ice sheet, the upland tributaries were left hanging five hundred feet or more above the overdeepened main-valley bottom, and the streams descending the steepened main-valley slope began to cut gorges in it. This condition lasted through interglacial times and resulted in the production of fairly broad and deep gorges. Then came a readvance of the ice, which again broadened and deepened the valleys and on its recession left the interglacial gorges, partly buried and erased, hanging high above the newly made bottom of the main valley. Since the retreat of the Wisconsin ice sheet the streams have been engaged again in gorge cutting on the steepened slope, in some places along the lines of the older gorges, but more commonly partly or completely independent of them.
There are some facts which indicate possible greater complexity of ice erosion, for in some of the valleys there is apparently more than one buried gorge; but the evidence on this point is not as yet convincing, and for the present we can point with certainty to no greater complexity than that of two periods, one the Wisconsin, the other of some one of the earlier ice advances with which the work of the glacial geologists of the Mississippi valley have made us familiar.
The various glens of the Cayuga and Seneca Lake valleys, whose general cause is as above stated, differ greatly in detail. They are all wild and picturesque, and they are all narrow gorges with many cascades and waterfalls. Their variations depend upon the varying combinations of effects from several causes. One of these is the influence of the buried gorges. Wherever the postglacial stream enters one of these its valley abruptly broadens. Where the postglacial course coincides with the buried gorge the expansion is continuous; but where it merely crosses the older gorge, the narrow rock-walled and rock-bottomed postglacial gorge is replaced by an expansion, forming an 'amphitheater' with drift walls and bottom. The valley again contracts where the stream leaves the buried gorge and has cut a postglacial glen in the rock of the other wall of the older gorge.A second cause for differences in the gorges is the influence of the variation in resistance to erosion of the nearly horizontal strata of Devonian shales and sandstones in which the gorges arc cut. The
Fig. 8. Greentree Falls in Six Mile Creek, near Ithaca, illustrating the influence of joint planes on gorge and waterfall form.
Fig. 9. Step Fall in Enfield (Butternut) Creek, southwest of Ithaca, illustrating the influence of horizontal strata on waterfall form.
sandstone layers retard erosion and form falls, sometimes single leaps, sometimes step falls (Fig. 9) where the water cascades from ledge to ledge. With the variable spacing of the sandstone and shale layers, there is almost infinite variety in waterfall form.The variation in gorge and waterfall form is still further increased by the joint planes which cleave the strata nearly vertically, and thus introduce a cause for vertical variation in erosion in addition to the horizontal. Some of the most beautiful of the cascades are those where the stream erosion has etched out combinations of horizontal and vertical irregularity in the rock bed over which the water falls (Fig. 8). The joint planes often guide the stream course between the falls also, sometimes confining it between narrow,
Fig. 10. Pot-holes, Watkins Glen.
canyon-like walls with smooth, straight sides, sometimes leading the stream into sharply rectangular courses where the water departs from one set of joints to the other, which extends at right angles. Both the horizontal stratification and the vertical joint planes also affect the outline of the gorge walls, giving rise to some striking and picturesque effects.
Still another feature prominently illustrated in these gorges is the pot-hole, formed where the cascading waters bore into the stream bed and. grinding pebbles about in the swirling waters, form large, deep pools (Fig. 10), adding interesting variety to the scenery of the gorges, which at every turn have some new feature of interest or beauty. All these varied phenomena, but best of all the pot-holes, are illustrated with great clearness and variety in the wonderfully picturesque Watkins Glen.
From the standpoint of either the geographer, the geologist or the lover of scenery, a visit to any of these glens is well worth one's while; but no single one is so easily accessible, nor presents such a variety of phenomena, as Watkins Glen. Nearer centers of population it would be far more famous than now. and would be visited by scores of thousands. Waterfalls and gorges in Europe which can not be compared in beauty or interest with a score of glens in the Finger Lake region are far better known to the traveling American than Watkins Glen. It seems well, therefore, that it should be taken by the state, made better known, and opened freely to the public.
- ↑ Published by permission of the director of the U. S. Geological Survey.
- ↑ This statement ought perhaps to be slightly qualified, since exceptional instances of hanging valleys have been described from such regions where other causes, such as marine erosion and faulting, account for the hanging valleys.
- ↑ Lincoln, Amer. Jour. Sci., Vol. XLIV., 1892, pp. 290-293; Tarr, Bull. Geol. Soc. Amer., Vol. V., 1894, pp. 339-356.
- ↑ Tarr, Bull. Geol. Soc. Amer., Vol. XVI., 1905. pp. 213-228.
- ↑ Tarr, Amer. Geol., Vol. XXXIII., 1904. pp. 271-291.
- ↑ Tarr, Jour. Geol., Vol. XIV., 1906, pp. 18-21.
- ↑ A deep well at Watkins, 1,080 feet in depth, did not reach the rock bottom of the valley, striking the side of a cliff and bending the tool so that further boring was impossible.
- ↑ For further description of these phenomena see Tarr, Bull. Amer. Geog. Soc., Vol. XXXVIL, 1905, pp. 193-212.