50 NEW YORK STATE MUSEUM 



and Triarthrus becki. These are also the most fre- 

 quent species, and the entire fauna receives thereby a distinct Cana- 

 joharie-Utica aspect. But we also note in the congeries of forms 

 a number of species that are not observed in either the Canajoharie 

 or the Utica, but are known only from the Trenton. Such spe- 

 cies are Lingula rectilateralis, Conularia 

 trentonensis, Spyroceras bilineatum, Tri- 

 nucleus concentricus, Eurychilina. It is 

 mainly the evidence from these fossils that indicates the Trenton 

 age of the Schenectady formation. Finally there is a strong ele- 

 ment of entirely new species, giving the Schenectady beds a distinct 

 character of its own; this element consists of a few rare species,. 

 as Dictyonema multiramosum, Taeni aster 

 schohariae, Saffordia ulrichi, and especially 

 of the eurypterids. It is true the Echinognathus 

 c 1 e V e 1 a n d i Walcott, of the Utica shale of Holland Patent, 

 N. Y., may be contained in this Schenectady fauna, and thus also 

 one eurypterid at least be a Utica element, but there is still no doubt 

 that the eurypterids of the Schenectady beds constitute a strong 

 distinctive feature from the Utica fauna as known to us at present. 

 If we attempt to compare this formation with others outside the 

 State, we find similar shale beds of upper Trenton age in the lower 

 third of the Martinsburg shale (title 62, page 62) in Penn- 

 sylvania, extending thence probably into the Martinsburg shale of 

 New Jersey and south into Maryland. 



INDIAN LADDER BEDS 



The best section known to us leading from the Schenectady beds 

 up to the Upper Siluric beds, is along the upper left branch of 

 Black creek forming the fall and deep ravine at the Indian Ladder 

 near Meadowdale, Albany county, N. Y. The section comprises 

 about 410 feet (aneroid measurement), of which the lowest lOO 

 feet are dark gray to black argillaceous shales with two thick sand- 

 stone bands (each about 4 feet), while the next 100 feet are of a 

 character not met with in other outcrops of the Schenectady beds.. 

 They consist of rapidly alternating dark gray shales and thin rusty 

 looking, somewhat calcareous sandstone layers, 5^ to i inch 

 or more thick. The uppermost part of this portion becomes 

 quite sandy. Nearly 100 feet are there covered, while some 120 feet 

 at the top consist of prevailingly heavy sandstone beds with inter- 

 calated dark arenaceous and argillaceous shales, and an occasional 



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