278 S. L. POWELL 



500 feet thick, which is as thick as the Trenton above, and main- 

 tains its individual character throughout, in respect to Hthol- 

 ogy as well as fossil content. While no decided break or hiatus 

 has been observed between it and the Trenton, yet there is a marked 

 change in sedimentation. The shale deposit ceases and limestone 

 appears, and along with it an entire change of life. Between it and 

 the formation below the change in sedimentation is still more 

 marked, for the fine black sediment of the Athens shale rests imme- 

 diately upon the thoroughly crystalline limestone and marble of 

 the Black River. The feature that would most closely associate 

 the Athens shale with the Trenton is the occurrence of Triarthrus 

 hecki in the shale, but while it has been reported from the Trenton 

 of other locahties, it has not been observed to occur in the Trenton 

 at this point. The Trenton here is singularly devoid of fossils. 

 Everything considered, conditions here point to the same conclu- 

 sion for the Athens shale as those reached by Lapworth, Ami, and 

 Ruedemann for the Normanskill of New York, viz., that it repre- 

 sents a distinct epoch of the Ordovician. 



The species of graptolites and other forms from the Athens shale 

 thus far determined are as follows: 



Climacograptus bicornis Hall 

 Climacograptus modestus 

 Climacograptus parvus Hall 

 Climacograptus putillus Hall, mut. eximus 

 Climacograptus putillus Hall 

 Climacograptus scalaris 

 Climacograptus typicalis Hall, mut. spinifer 

 Climacograptus scharenbergi Lapworth 

 Corynoides gracilis Hop., mut. perungulatus 

 Cryptograptus tricornis Carruthers 

 Dicellograptus sextans Hall 

 Dicellograptus intortus Lapworth 

 Dicranograptus spinifer Lapworth 

 Dicranograptus nicholsoni Hopkins 

 Dicranograptus ramosus Hall 

 Didymograptus serratulus Hall 

 Didymograptus sagittacauHs Gurley 

 Didymograptus subtenuis Hall 

 Diplograptus amplexicauHs Hall 

 Diplograptus angustifolius Hall 



