No. 136.] 65 



York, as yet, only from Marcellus to Schoharie ; but it is probable 

 that they may be found well developed through the Helderbergs 

 and along the hills west of the Hudson river and Delaware and 

 Hudson canal to Pennsylvania. The layer is easily found, gene- 

 rally projecting in ravines worn in the shale not far from its 

 base ; and it is hoped that this pamphlet may stimulate some 

 readers residing in that district to look for it, and collect its 

 many fossils. 



The Marcellus shales change gradually, at their higher part, 

 into the 



HAMILTON GROUP, 



which is a harder, lighter-colored mass, often becoming a sand- 

 stone, and, in Central New- York and as far east as the Catskill 

 range, is a thousand feet or even more in thickness. Like the 

 Marcellus shale, many parts of it show very little marks of 

 stratification ; but it is divided perpendicularly by joints, which, 

 where it is excavated, often show as upright and smooth as the 

 walls or angles of a plastered building. In the more eastern 

 part of the State, it is generally coarse-grained and sandy : in 

 Western New-York, it is fine grained, soft, and more calcareous, 

 forming by its decomposition a rich soil. 



Taken as a whole, it is exceedingly prolific in fossils, though 

 in some of its beds they are few. They are very various in their 

 nature, comprising univalve, bivalve and chambered shells, corals, 

 trilobites, crinoids, fish-bones, and distinct remains of land 

 plants; being the lowest and oldest rock in New-York in which 

 any traces of terrestrial vegetation have been found, except a few 

 indistinct stems in the Marcellus slate (a fragment of this kind 

 is shown in Fig. 34a). 



Four or five species of Trilobites are known : the largest 

 (which is common in Centi;al New-York, but rare further west) 

 is the Homalonotus dekayi; which, in general appearance as well 

 as size, resembles the Homalonotus from the Niagara shale (Fig. 

 29). It differs, however, in the form of the head ; and the plate 

 covering the other extremity, instead of being furrowed trans- 

 versely and pointed at the end, is smooth and rounded. The 

 Phacops bufo (Fig. 30, No. 6) is a small trilobite abundant in 

 many places, especially near Moscow in Livingston county, and 

 near Eighteen-mile creek in Erie county : many specimens show 

 [Assembly, No. 136.] 9 



