ARTESIAN WELL SECTIONS AT ITHACA, N. V. 79 



Pi?ms rigida ; (2) Millard Well No. i, 50 feet, gravel, the com- 

 mon tamarack, Larix americaiia. Dr. Dall reports that the mol- 

 lusca belong to the following genera: Valvata, Planorbis, Amni- 

 cola, and fragments of Pisidium or Sphcerium. These are 



all of the same nature, namely fresh-water, and such as are found in the con- 

 fervae or other fine-textured vegetable matter, such as grow in quiet places 

 in the course of brooks, or in ponds or lakes at the mouth of brooks. They 

 would hardly be found in the unsheltered waters of a large lake like Lake Erie. 



Correlation of coarse sedim.e?its with Iroquois stage. — The evidence 

 seems conclusive that these sands and gravels were either 

 shallow-water, lake-margin deposits or else stream-made land 

 deposits, and that they were succeeded by lake conditions. In 

 seeking for an explanation of these phenomena, land-tilting 

 seems the only rational hypothesis. It is a well-known fact, as 

 clearly shown by Dr. Gilbert, that the land has been tilted in 

 this region since the deposit of the beaches of the Iroquois shore 

 line. The Iroquois lake stage immediately succeeded the stage 

 of ice-dammed lake in Cayuga Valley. Therefore these sands 

 and gravels are in the right position for correlation with the 

 Iroquois beach stage. 



In a letter to me Dr. Gilbert supplies the following informa- 

 tion : Correlating the upper bar at Richland Junction (563 feet) 

 with the lowest bar at Weedsport, there is a gradient of 2.g feet 

 per mile. Correlating the upper Richland bar with the lower cut 

 terrace at Montezuma, there is a gradient of 2.6 feet per mile. 

 Correlating the upper Richland bar with a bar at Cayuga, there 

 is a gradient of 2.7 feet per mile. 



The lines on which these measurements are made do not precisely corres- 

 pond with the direction of greatest slope of the plane of deformation, but I 

 judge that the line from Union Springs to Ithaca makes about the same angle 

 with the direction of greatest slope, so that these figures might be applied 

 without correction. A correction for direction would increase the estimates 

 for gradient. 



From Union Springs, where the Iroquois beach disappears 

 beneath Lake Cayuga, to the site of the wells is approximately 

 twenty-nine miles; and, taking 2.7 feet per mile as a gradient, 

 the Iroquois shore line might be expected to appear at Ithaca at 

 a depth below present lake-level of about 78 feet. Several of 



