292 New York State Museum 



out of the State as a concealed formation. It has a 

 maximum thickness of about 100 feet. 



The Indian Ladder beds (Ruedemann T2) are typi- 

 cally exposed in the Black creek ravine, Indian Ladder, 

 Albany county, hence the name (figure 52). These beds 

 extend from there, rapidly thinning below the Helderberg 

 escarpment, to the north and to the south. They disap- 

 pear a short distance south of the village of New Salem 

 on the south, and on the north only a few feet are found 

 after crossing the Altamont-Knox state road. The In- 

 dian Ladder beds have a thickness of over 400 feet of 

 which the lower hundred feet are dark gray to black ar- 

 gillaceous shales with two heavy sandstone beds. Above 

 this are alternating gray shales and thin, yellow, rusty- 

 looking, calcareous sandstone bands, which are very 

 characteristic. The uppermost portion becomes quite 

 sandy, consisting in the upper hundred feet or so of pre- 

 vailing heavy sandstone beds with interbedded dark are- 

 naceous or argillaceous shales and sometimes a limestone 

 band. This formation is on the whole quite barren. 

 Graptolites, as Dictyonema arbusculum and Dicrano- 

 graptus nicholsoni have been found in the shales, but the 

 calcareous sandstone bands have yielded the larger fauna, 

 in which are included the bryozoan Hallopora onealli, 

 the brachiopods Dalmanella multisecta, Rafinesquina 

 tdrichi and Plectambonites centric arinatus, the ostracod 

 Ceratopsis chambersi and the trilobites Cryptolithus bel- 

 hdus and Odontopleura crosota. The fauna of the In- 

 dian Ladder beds is not represented anywhere else in 

 eastern New York; the beds are of Cincinnatian 

 (Frankfort) age. This, together with the restricted 

 horizontal (east and west) distribution, suggests that 

 the Indian Ladder beds were deposited in an inde- 



