144 S. G. Williams — Bocks of Lower Helderberg Age. 



of strata, including at leapt a portion of the gray beds, it does 

 not seem possible to separate these groups definitely, while 

 nothing answering to the Upper Pentamerus occurs here. 



This description of the Lower Helderberg at Oriskany Falls 

 has been given to call attention to the fact that a series which 

 in Schoharie and Albany Counties presents four strongly 

 marked changes in rock characters, accompanied by consid- 

 erable differences in the grouping of specific forms, has here, 

 with some apparent diminution of total thickness, become of 

 much more uniform lithological character, even the gray lime- 

 stones which crown the series lacking that massive and rough- 

 weathering appearance which is so prominent at the east; and 

 that this simplification of rock characters is accompanied by a 

 tendency to obliteration of any definite divisions characterized 

 by distinctive groups of fossils, the Tentaculite limestone hori- 

 zon only being here clearly marked, and showing a tendency 

 to retain its dominant life characters after the individuality of 

 the other divisions has been lost by the blending of their 

 faunas. In the Skaneateles section, as has already been seen, 

 the life of the Tentaculite Lime only is represented, with the 

 exception of Favosites ffelderbergice, and the beds worked for 

 hydraulic lime occur near the summit of the series; while on 

 Cayuga Lake the seventy feet of limestones to which the Lower 

 Helderberg, exclusive of the Water-lime, is there reduced, have 

 all subdivisions quite obliterated, contain Stromatopora at two 

 different levels and probably at three, and x while retaining two 

 or three common fossils of the Tentaculite, vindicate their 

 right to represent a large portion if not the whole of the Lower 

 Helderberg period by containing a considerable number of its 

 characteristic forms, including Platyceras, unmixed with any 

 Water-lime species, as well as by lying above strata holding 

 Eurypterus and Leperditia alia. 



It may be remarked that the three sections that have here 

 been given, as well as the widely-known series in Schoharie 

 County with which they have been compared, all have well- 

 developed Oriskany sandstone to mark their upper limit, show- 

 ing the probability that all are equally complete as they were 

 deposited, and if so, that all are probably synchronous since 

 they are all equally free from any indications of having been 

 withdrawn from deposition by becoming land areas. If this 

 be true, their differences both of lithology and life must be due 

 to differences in circumstances of deposition in different por- 

 tions of the same long Silurian coast-line. Indeed, when it is 

 considered that the Onondaga Salt series, which is very thick 

 in Ontario and in Western and Central New York, thins out 

 entirely in the east : that the non-saliferous representative of 

 the Onondaga (Salina) in Pennsylvania has, in a portion of its 



