THE ORDOVICIAN PERIOD. 



311 



The above subdivisions of the system indicate that successive 

 epochs of longer or shorter duration gave rise to recognizable differ- 

 ences in sedimentation, and that these differences in sedimentation 

 were accompanied by faunal changes, usually not profound. The gen- 

 eral conformity between the several formations of the system, and 

 the conformity of the lowest with the Cambrian, shows that great geo- 

 graphic changes did not affect the region of New York while the Ordo- 

 vician strata were in process of deposition. Locally, beds corresponding 



Fig. 130. — Chazy limestone. From Phelps Point, Grand Isle, Vt. 

 Shows Strephochetus oscellatus. 



to the Chazy are wanting, but even in such areas there is only a mod- 

 erate unconformity between the Beekmantown formation and the 

 Middle Orclovician series. The land surface of the Chazy epoch, where 

 there was land, seems therefore to have been low and subject to little 

 erosion. 



The lowest formation in New York (the Calciferous or Beekmantown) is 

 an impure limestone, or sometimes a calciferous sandstone. During its depo- 

 sition, the general relations of land and sea remained much as in the late Cam- 

 brian. After it had attained a thickness of a few hundred feet, change of rela- 

 tions affected much of the Appalachian trough, converting into land considerable 

 areas which had been submerged. After these disturbances had taken place; 

 the only part of New York known to have remained under water is an area in 

 the extreme northeastern part of the state, to which a bay from the Atlantic 

 reached. In this bay the sediments of the Chazy formation were deposited. 



