GEOLOGY AND PALEONTOLOGY OF THE SCHOHARIE VALLEY 



111 



Fig. 18 Leper ditia scalaris 

 (enlarged ) 



metric bivalve. The cephalopods are represented by T r o c h - 

 o c e r a s g e b h a r d i [fig. 

 16, 17] which coils so as to 

 resemble a large gastropod. 

 Crustacea are represented 

 chiefly by the two large spe- 

 cies of ostracods Leper- 

 ditia jonesi and L . 

 scalaris [fig. 18], the lat- 

 ter with a swelling on the hinge 

 margin not found in L . jonesi. Trilobites (Calymmene, Dal- 

 manites, Lichas etc.) are also found. 



The Eondoiit and Manlius limestones 



The Coblesldll bed is succeeded by a series of more or less 

 uniformly and finely bedded lime mudrocks with occasional lime 

 sandrocks which form a deposit averaging 60 feet in thickness 

 in the Schoharie region. The name Rondout limestone is applied 

 to tlie lower portion from the extensive cement-mining opera- 

 lions which are carried on in this formation near Rondout N. Y. 

 At that locality the upper beds included in the formation are 

 not used for cement. They show a remarkable series of mud- 

 crack structures of pentagonal form which very clearly indicate 

 that this rock was a fine lime mud, probably exposed at low 

 tide to the drying influence of the sun. Though not common at 

 Schoharie this structure has been found in blocks of Rondout 

 limestone on West hill. 



The only place in the Schoharie region where the cement beds 

 of the Rondout are mined is at Howes Cave. Here the lowest 

 6 feet of the Rondout formation are mined in tunnels hj the 

 Helderberg Cement Co. for the manufacture of natural or Rosen- 

 dale cement [pi. 7]. The application of the latter term to the 

 cement here mined is merely a commercial practice; the bed 

 mined is not the stratigraphic equivalent of the Rosendale 

 cement bed (the lower bed mined at Rosendale) but of the upper 

 or the one to which the name Rondout is applied. At Howes Cave 



