52 NEW YORK STATE MUSEUM 



them US Hall and small cranidia of a Dalmanites (Pterygo- 

 metopus). 



Doctor Ulrich has determined the horizon as corresponding to 

 the lower third of the Southgate shale of the Eden group at Cincin 

 nati. 



A comparison of the fossil list here given with that of the 

 Schenectady beds shows at once that the " Frankfort " beds of the 

 lower Mohawk valley contain two distinct faunas. The beds at 

 the Indian Ladder also differ in their lithologic aspect; it is there- 

 fore safe to distinguish them as . a separate! unit, for which the 

 name Indian Ladder beds is here proposed. 



The Indian Ladder fauna is markedly distinct from the Schenec- 

 tady fauna in the absence of all the dominant forms of the latter, 

 as notably the eurypterids, Climacograptus typi- 

 calis, Triarthrus becki, Trocholites ammo- 

 n i u s and the seaweeds. It consists on the other hand of a 

 congeries that has hardly any members in common with the Sche- 

 nectady beds. Much of this is clearly due to a different facies or 

 different marine conditions, at least in the contents of the rusty lime- 

 stone bands ; for instead of the mud-loving linguloids and lamelli- 

 branchs of the Schenectady beds, we find here the strophomenoids 

 and orthoids, indicating clearer water. The novel element of this 

 faunule is represented principally by bryozoans, brachiopods, the 

 ostracod Ceratopsis chambersi and the trilobites 

 (Acidapsis crossota, Trinucleus bellu- 



1 u s ) and the reappearance of such Trenton forms as 

 Dalmanites callicephalus and Ceraurus 

 pleurexanthemus. Also the graptolite faunule of the 

 shale is totally different from that of the Schenectady beds. In 

 Dicranograptus nicholsoni it contains an upper 

 Trenton and lower Utica element, that here reappears after a long 

 interval, in Diplograptus peosta, the first fore- 

 runner of the Lorraine fauna and in Dictyonema arbus- 

 c u 1 a , a form of the middle Eden shale of Ohio. The combined 

 evidence of the whole fauna is that the Indian Ladder beds are 

 younger than the Schenectady beds, not a mere different facies of 

 the same, but still older than the typical Lorraine. 



The horizontal extension of the Indian Ladder beds in the expos- 

 ures at the base of the Helderberg escarpment seems to be but very 

 restricted. In the section obtained along the roads south of 

 Altamont, only four miles west of the Indian Ladder, 



J 



