158 Forty- SIXTH Report on the State Museum. 



from the observations of Mr. Yanuxem that the Lower Helder- 

 berg group had its western termination about the longitude 

 of Auburn or the eastern shore of Cayuga Lake, and it is in this 

 neighborhood that Prof. S. G. Williams has shown that the lower 

 members of the group do mingle, and alternate with the Water- 

 lime and the marls of the upper portions of the salt group. At 

 numerous localities similar conditions may be observed where 

 the magnesian sediments of the Waterlime and associated marls 

 have encroached upon the sea bottom in which the lower Helder- 

 berg limestone were being deposited and the sediments of these 

 two formations have become mingled or alternated in deposition. 

 At Howe's Cave, Schoharie and other places it is not uncommon 

 to see the dark blue Tentaculite limestone in layers of one- 

 quarter or one-half an inch in thickness alternating with 

 the drab colored Waterlime in laminae of equal thickness. This 

 alternation continues through several feet of thickness, the blue 

 Tentaculite layers gradually growing thicker and the drab 

 Waterlime proportionally thinner till these beds of passage are 

 passed and we have the Tentaculite limestone gradually passing 

 into thick heavy bedded layers of dark blue limestone, which on 

 polishing becomes a fine black marble. In going farther west- 

 ward this distinct alternation of beds is not so marked, but 

 instead a gradual mingling of the two sediments while in process 

 of deposition. 



In going westward from Cayuga Lake outcrops of the Lower 

 Helderberg have rarely been found showing satisfactory evi- 

 dences of the age by the presence of fossils through the beds 

 many 3^ears ago doubtfully referred to this horizon in Ontario 

 county have proved to be part of the formation. Later evidences 

 coming from the well borings and especially from the excavations 

 of the Livonia salt shaft have shown that the lower members of 

 the Helderberg limestone with its fauna represented in a few of 

 the characteristic fossils extend much further to the westward 

 than we had heretofore supposed. 



The results in detail of this geological exploration will be com- 

 municated together with the portions of the map in which the 

 limits and extent of the geological formations explored will be 

 laid down. 



