GEOLOGY AND PALEONTOLOGY OF THE SCHOHARIE VALLEY 



123 



took place, subsidence of the sea floor and consequent advance of 

 the shore taking the place of elevation and retreat of the shore. 

 This advance of the shore brought with it a second working 

 over of the conglomerates which gradually crept on to the shore 

 again, covering the previously eroded surfaces. While this took 

 place the finer material, much oxidized, was carried seaward, 

 i. e. westward, and deposited above the Oswego sandstone as 

 the red Medina mud, wmich now constitutes the shale 1100 feet 

 thick in western New York. Now, while the deposition of these 

 shales went on the shore gradually advanced and with it the 

 conglomerates. But obviously these advancing conglomerates, 

 though continuous with the Oneida conglomerate, became of later 

 and later age, and corresponded in time to the red Medina shales 

 of western New York [fig. 28C]. It is thus evident that 

 these later conglomerates can not be called the Oneida, as is 

 generally done, since they are of Postoneida age. The term 

 basal conglomerates or Shawangunk conglomerate, the latter 

 being applied to a portion of the basal conglomerate in the Shaw- 

 angunk mountains, wmich is most certainly of Salina age, may 

 be used in a general discussion of this lithic but not stratigraphic 

 unit. Toward the end of the deposition of the 1100 feet of 

 Medina shales there was another spreading out of the shore 

 strata, which caused the formation of the quartzose bed that 

 abruptly overlies the Medina shales at Niagara. 1 Then came 

 the deposition of the Medina sandstones, which indicates shallow 

 water, an idea borne out by Hie ripple marks and wave marks on 

 these rocks. To the west of Lake Michigan the Medina and 

 Osw ego are both absent or bnt slightly represented. This may be 

 due to the existence of land conditions in thai region, in which 

 case we should expect shore deposits in Hie thin western edge of 

 the Medina. Or the Mayville lime sandrock may have accumu- 

 lated during Medina time in Hie western purer water. This seems 



l 8ee Geology and Paleontology of Niagara Falls and Vicinity. N. Y. 

 State Mus. Bui. 45. 1901. p. 88. 



