28 



some little distance above the, fall formed by the oiiterop of 

 the Encrinal limestone. The len_^th of the section below 

 the fall is about 2200 feet, and the chord of the crescent de- 

 scribed by it, extends approximately, east 20 degrees north, 

 b\' west 20 degrees south, which is about the direction of the 

 strike of the strata in this region. This accounts for the fact 

 that the strata appear horizontal in the section. The dip 

 may be observed at the fall near the head of the section. On 

 the right side of the fall the limestone commonly projects 

 above the water, while on the left side it is a foot or more 

 below the ordinary water level. 



In the section appear representatives of the strata from 

 the black Naples (Gardeau) shales to the Hamilton shales. 

 The former are represented b\' their lower five or ten feet 

 only, which form a vertical face under the influence of the 

 perfect jointing developed in them. The gray Naples or 

 Cashaqua shales are represented in their entirety, and form 

 a more or less sloping bank under the vertical cliff of 

 Gardeau shales. Beneath the gra}' Naples shales, another 

 vertical cliff is formed by the black Genesee shales, which in 

 many places overhang the rock below, presenting smooth 

 joint faces, and projecting prisms and parallelepipedons, 

 nearly separated from the main wall and dangerously in- 

 secure. Frec[uent falls of rock from a height of about thirty 

 feet, furnish abundant material for examination, at the same 

 time making the collecting of the fossils from the extremelv 

 rich Hamilton fauna at the base of the cliff, a hazardous 

 undertaking. 



The Genesee shales in their fresh condition, are heavy 

 bedded, and large blocks will hold together cjuite iirmh'. On 

 weathering, however, probabh' by the oxidation of the 

 pyrite gi^ains which are plentifully scattered through the 

 rock, they become more fissile, so that ultimately large slabs 

 of excessive thinness can be readily separated. It is probable 

 that the pyrite grains are spread more thickly on the bed- 

 ding planes, or at any rate that they are most prone to 



