380 



M. L. FULLER — GEOLOGY OF FISHERS ISLAND 



true clay, and are always decidedly gritty to the teeth, and usually to 

 the touch. Nevertheless they so partake of the characteristics of the 

 Gardiner clay that they are readily mistaken for it at first sight. They 

 appear, however, to mark a distinct change in conditions, and hence 

 are made a separate formation. Interbedded with the finer varieties of 

 the Jacob deposits there are some more distinctly sandy beds, usually 

 buff or yellowish in color and several feet in thickness, in which particles 

 of fairly fresh granitic minerals can be recognized. 



Upward the deposits give place to medium and finally to coarse 

 sands, which in turn give way to the Herod gravels, the intermediate 

 sands being in fact transitional between the two formations. 



Details of occurrence. — The best exposures of the Jacob sands are to 

 be seen in the clay pit (figure 6) in the sections at Isabella beach (figures 

 7 and 8). In the pit, as already stated, there are 40 feet of brownish 



Figure 10. — Artificial Section Exposed in June, 190K, near Steamboat Landing on West Side of West 



Harbor. 



a, till (Montauk ?) ; b, gravel (Herod ?); c, gray clayey sand (Jacob ?); d, gravel (probably lens in 



Jacob sand). 



sandy clay of a chocolate tinge, interlaminated with sands overlying the 

 darker and more plastic Gardiner clay into which they grade. At the 

 first of the Isabella Beach localities the Jacob sands are represented by 

 some 15 feet of fine gray clayey sand intervening between the Gardiner 

 clay and the Herod gravels (figure 7), while at the second some 35 feet 

 are represented with the top unexposed (figure 8). Of this 35 feet the 

 lower 15 are of the usual gray-green claj^ey sand type, but the upper 22 

 feet approach a gray sandy clay in character. In an artificial cut near 

 the steamboat wharf on the west side of West harbor a considerable 

 amount of grayish clayey sand of the Jacob type is exposed, as shown 

 in figure 10. The relations in the right-hand half of the figure, especially 

 the upturning and unconformity, are especially characteristic of the con- 

 ditions at the Jacob horizon in Long island and eastward ; but nowhere 

 else save at Sankaty head, Nantucket, has a gravel been seen interbedded 

 with the sands, as shown in the left-hand portion of the figure. There 

 is also somewhat less of the "old look," characteristic of most exposures 

 of the drift of this stage, but this may be due to the freshness of the artifi- 

 cial exposure. The topography, moreover, has a distinctly pre- Wisconsin 

 aspect, and the overlying till resembles the Montauk drift ratrfer than 



