LOWER SILURIC SHALES OF THE MOHAWK VALLEY 9 



Walcott (title 9) in his " Utica Slate and Related Formations," 

 distinguished the Utica epoch from the Trenton and Hudson River 

 epochs and added a considerable number of new types (two species 

 of the sponge genus Cyathophycus, species of graptolites of the 

 genus Dendrograptus, Leptograptus annectans and 

 a few other forms) to the list of hitherto known Utica species. In 

 his " Catalogue of Fossils Occurring in the Utica Slate " (page 34), 

 he brought the Nonnanskill shale with its graptolites into the Utica 

 shale as an upper division. The geographic distribution of the 

 Utica shale within and outside of New York was fully discussed by 

 him. The presence of passage beds between the Trenton lime- 

 stone and Utica slate in the region of the type section is also 

 commented upon (page 10). The thickness of the Utica shale, 

 before greatly underestimated, is given as over 600 feet at the type 

 section. 



Beecher published in 1883 (title 13) a list of fossils from the 

 black shales near the old Dudley Observatory, at Albany, referring 

 the beds to the Utica epoch and Ford, a year later, recorded the 

 discovery of a few fossils (Graptolithus pristis, Gr. 

 mucronat.us, Triarthrus becki and L i n g u 1 a 

 c u r t a ) in the slaty and arenaceous rocks in the vicinity of 

 Schenectady, which on the strength of this evidence he also consid- 

 ers as of Utica age, while the preceding authors (Vanuxem) had 

 referred it to the Frankfort slate, respectively Hudson River shale 

 (Mather, Emmons). 



In 1890, Walcott in a paper on " The Value of the Term Hudson 

 River Group," asserted the continuation of both the Utica slate 

 and Frankfort shale into the Hudson valley, thereupon basing his 

 argument for the extension of the term " Hudson River group " 

 to all beds between the Trenton limestone and Upper Siluric. As 

 before, he included the Normanskill shale in the upper Utica epoch 

 or lower Frankfort. The fauna discovered by Beecher at the 

 Dudley Observatory was correlated with the upper Utica and that 

 from the glazed slates at Cohoes (whence Hall in Palaeontology of 

 New York, volume i , reports Ambonychia radiata, 

 etc.) to the Frankfort shale. The important fact is pointed out 

 that a well drilled at Altamont (Knowersville), 17 miles west 

 of Albany, gave a thickness of 3475 feet for the strata between 

 the Lower Helderberg limestone and the Trenton limestone. On 

 account of its proximity this section allows a good estimate of 

 the great thickness of the Utica and Frankfort shales in the lower 



