NIAGARA FALLS AXD VTCINITY 35 



these deposits, particularly the limestones, point to a considerable 

 distance from the shore line, we are by no means at liberty to as- 

 sume that no shore formations accumulated during this period. In 

 fact, it would be difficult to understand the non-accumulation of ter- 

 rigenous material along the shores of any land during any period of 

 the earth's history unless such land was wi-thout even moderate 

 relief. As will be shown in chapter 3 there are reasons for suppos- 

 ing that a considerable land barrier existed in the north as well 

 as the east and southeast, and thus we may assume that shore de- 

 posits of terrigenous material were formed while the limestones were 

 accumulating in the clearer waters. That the shores of this period 

 did not consist of Medina sandstone is indicated by the absence of 

 any such material in the shales of either the Clinton or Niagara 

 series. It is highly probable that the shore was still formed by the 

 old crystalline highlands, and that the accumulating Clinton and 

 Niagara sediments overlapped and completely buried the A/fedina 

 beds. The limestones are chiefly fragmental in origin, being com- 

 posed of calcareous and magnesian sands. These, as will be shown 

 later, were largely derived from the destruction of coral reefs and 

 shells growing in the immediate neighborhood. They indicate shal- 

 low water^ a conclusion emphasized by the occurrence of well 

 marked cross-bedding structure in some of the beds of limestone. 

 We may assume a gradual passage from pure calcareous beds to 

 beds consisting more and more of terrigenous detritus as we ap- 

 proach the old shore line, where quartz sands probably constituted 

 the chief material of the deposits. 



We may obtain an approximate indication of the former extent 

 of these strata if an attempt be made to restore the portions which 

 must have been removed by erosion. We may consider the Clinton 

 and Niagara as a unit, assuming that near the old shore their beds 

 were practicably indistinguishable. The average dip of the strata 

 of this region is 25 feet to the mile (a moderate estimate, as the dip 

 ranges up to 40 feet), and the base of the Clinton-Niagara is ap- 

 proximately 400 feet above sea level. Continuing this dip north- 

 ward for a hundred miles to where the present borders of the old- 

 land are exposed, the base of this group would have risen 2900 feet 



