O NEW YORK STATE MUSEUM 



It was further found that beds formerly considered by the 

 author (op. cit., page 29) as representing one formation (the 

 Magog), had to be divided into two units, the Canajoharie shale and 

 the Snake Hill beds. These beds are not only in juxtaposition 

 about the mouth of the Mohawk, but even intermingled in that 

 much-folded territory, and we originally considered them as both 

 belonging to the Mohawk series and therefore have described also 

 the Snake Hill beds in this paper. Later work has, however, shown 

 that the Snake Hill beds were deposited in the Levis basin upon the 

 Normanskill shale and have been brought to the mouth of the Mo- 

 hawk and in contact with the Canajoharie beds by the overthrusting 

 and compression of the shales of the Levis basin. We have never- 

 theless added the description of the Snake Hill fauna in the present 

 paper, first, on account of its present occurrence in the lowest 

 Mohawk valley, then, because of the intermixture of Snake Hill 

 beds with Canajoharie shale, and, finally, because of the fauna! 

 similarities suggesting their equivalence. The Snake Hill forma- 

 tion finds, however, its principal development in the area of the 

 Schuylerville sheet, and will therefore be more fully described 

 in the report on that region, soon to be published. 



Evidence was soon obtained that the lower part of the Utica 

 shale of the lower Mohawk valley is older than the typical Utica 

 shale and probably of Trenton age, and it would have been desirable 

 to also trace the Trenton limestone from its type section at Trenton 

 Falls to its much smaller section in the lower Mohawk valley. Time 

 was lacking for this undertaking but fortunately Doctor Ulrich has 

 furnished us important data as to the Trenton limestone, and we 

 are glad to acknowledge here our obligation to him not only for this 

 information, but also for advice in the identification of fossils, and 

 many valuable suggestions as to the broader bearings of the 

 problem. 



We are also under obligation to Mr David White for the valuable 

 notes on the interesting seaweeds collected in the Schenectady shale 

 (see page 73), to Prof. Bashford Dean, Dr L. P. Gratacap, Dr 

 H. A. Pilsbry for advising us in regard to the problematic fossils 

 from the Schenectady shale, here described (see page 74), to Prof. 

 A. F. Foerste for information regarding certain brachiopods and to 

 Dr E. O. Hovey for the loan of type specimens from the American 

 Museum of Natural History. 



