346 New York State Museum 



(Indian Ladder) there are about 14^2 feet of so-called 

 transitional beds below the Coeymans limestone which 

 are included in the measurement. The Manlius lime- 

 stone shows features, such as mud cracks and faint ripple 

 marks, that clearly indicate tide-flat conditions. This 

 limestone is also characterized in the upper part by heavy 

 Stromatopora beds (Syringostoma barrctti). These 

 reefs, together with the mud cracks, ripple marks etc. 

 suggest that the Manlius limestone is a lagoon deposi T 

 on tide flats formed between and behind the coral reefs 

 (Ruedemann '30). The fauna of the Manlius is a meager 

 one. The characteristic fossils are the pteropod Tenta- 

 culites gyracanthus which occurs in great abundance in 

 certain layers, the ostracod Leperditia alta, and the 

 brachiopod Spirifer vanuxemi. In the transition beds 

 the small brachiopods Stropheodonta varistriata and 

 Camarotoechia semiplicata are found. 



The Lower Helderberg beds in the early days of the 

 Survey were classed with the Silurian. Later the Siluro- 

 Devonian boundary was changed (Clarke) and the 

 Lower Helderberg limestones with the exception of the 

 Manlius were placed in the Lower Devonian. The Man- 

 lius, because of the rather Silurian aspect of its meager 

 fauna was left in the Silurian and since then has been 

 the subject of much discussion as to its age. Some, fol- 

 lowing Clarke, class the entire Manlius as Silurian, others 

 would place it with the Devonian and a third group 

 place the dividing line within the Manlius. According 

 to the last view the lower portion of Manlius exposed 

 in the Helderberg- Schoharie area represents the lower 

 beds and is the typical Manlius, Silurian in age. The 



