50 



11 lime is ])rcsciil. in llie slialcs, this will react with the icrric stilpliatc 

 to form calcitim sulphate jiiul ferric oxide; the latter bciiii; insoluble, 

 will be deposited where formed." The reaction is: 



Fe,,(S OJ, 3 Ca CO, - 3 Ca S O, - Fe-.O, 3 CO,. 



The calcium sulphide will be hydrated and deposited as yjypsum, as was 

 noted ill some portions of the ii])per Moscow shales. 



The ferrous sulphate may react directly with the calcium carbonate of 

 the shales, giving calcium sul])hate and ferric carbonate. The former 

 is hydrated and deposited as gypsum, while the ferrous carbonate is 

 carried off in solution. This may account for the absence of ninch iron 

 stain on the shales in which the gypsum crystals are formed. Eventu- 

 ally on exposure to the jitmosphere, the ferrous carbonate will oxidize 

 to insoluble ferric hydriite, whicli will l)c dei)osited. 



Concretions are not tinconiinon in this shale. They are 

 ttsually of iron pvrite, or at least have a pyrite nucleus. 

 Occasionally they have a se])tarian structure, with veins of 

 crystalline calcite, siderite, or more rarely, barite. The gray 

 Naples or Cashaqua shales, appear between the Genesee 

 below, and the black Naples or Gardeau shales above. They 

 are readilv recognized by their gray color, the numerous 

 rows of concretions, and the sloping, more or less weathered 

 face which they present. The rocks above and below form 

 perpendictilar banks, and consequently whatever vegetation 

 grows on the face of the cliff, is chiefly confined to the por- 

 tion formed by the Cashaqua shales. The upper ( Gardeau ) 

 shales, are exposed in the first half mile of the clift, after 

 which they are absent for a greater distance, the banks 

 decreasing to less than half their original height. 



This decrease in height begins at the "uplift," a thrust 

 fault of considerable magnitude, when the general undis- 

 turbed character of the strata of this region is taken into 

 consideration. The fault appears in a recession of the bank, 

 which is dtie to the weakening of the strata by the fault, and 

 conse([uently the greater readiness Avith which they succumb 

 to the attack of the waves. The vertical displacement ol the 



*In this manner shells arc ol'tt-n entirely rcplaceil by linionite. 



