ARTESIAN WELL SECTIONS AT ITHACA, N. V. 8 I 



land surface at the site of these wells was then from 6o to 120 

 feet below the present delta surface ; but, owing to the depression 

 of the land in the north, the lake waters either could not then 

 reach this far, or, if they did, produced only a shallow lake. At 

 this stage trees grew and moUusca thrived, while a series of sand 

 and gravel layers were laid down whose depth in the several 

 wells varies from 20 to 70 feet. 



Elevation of the land in the north tilted the basin of Lake 

 Cayuga faster than the deposit of sand and gravel was made, 

 ultimately covering the coarse deposits with lake water. Some 

 of the sand and gravel may be due to the work of the lake 

 waves as the tilting of the land caused an encroachment of 

 Lake Cayuga farther and farther south. The fact that the pres- 

 ent surface of the delta contains no sand and gravel excepting 

 near the stream mouths, may be explained as follows: (i) the 

 levelness of the delta ; (2) the recency of the delta — it is still so 

 swampy at the well sites that it is flooded at least once each 

 year; (3) the fact that the streams now bring less material, 

 having already cut through the drift into the rock. 



SOURCE OF THE ARTESIAN WATER. 



It is believed that the source of the water in the upper 

 gravels is the alluvial fans opposite the mouths of the streams 

 that descend to the Ithaca delta. Into these fans much of the 

 stream water sinks, in some cases entirely disappearing at all 

 times excepting in periods of flood. It is not absolutely certain 

 that the gravels of the alluvial fans are continuous with the sand- 

 gravel series encountered in the shallower artesian wells; but this 

 is to be expected, since the conditions which favor the deposit of 

 coarse sediment must have existed continuously near the mouths 

 of the streams that descend the hill slope. Some such source 

 near at hand is indicated by several facts: (i) a reported vari- 

 ability in volume; (2) the moderate pressure of the wells, which 

 in some cases barely forces the water from the ground; (3) the 

 composition of the water, which indicates a shorter underground 

 journey than that of the water in the deep wells; (4) the 

 marked difference in composition and purity of the water from 

 various wells. 



