1 SS CATSKILL DIVISION. 



I , (logically this is an interesting pari of ihr New- York series. It forms by itself a dis- 

 tinct system, and has been described by Mr. Pliillips undei the name of Devonian system. 

 Ii is designed to embrace not only the peculiar rocks of Devonshire, !>ut those of Scotland, 

 and of places on the continent, which have hitherto been known and described under the 

 name of Old Red sandstone. Comparing <>ur rocks of this division, however, with what 

 we know of their equivalents in Europe, we find that they present a different phase; re- 

 serving, m tins expression of opinion at this time, the right to change our views from time 

 to time as discoveries may progress. In Scotland, for instance, the Old Red sandstone 

 contains many fishes of remarkahle forms; hut in no place in this country, where this 

 rock is even well developed, have these interesting fossils been found. Here, conchifera, 

 -- iciated with a few fishes, seem to characterize the rock ; and these are confined to the 

 lower beds, the upper ones, so far as discoveries have been made, being destitute of animal 

 remains. Some land vegetables, belonging to three or four species, run through the sys- 

 tem. In thi- country, whatever differences may have been observed between the Hamilton 

 shales and the masses intervening between them and the Coal series, there is no where a 

 sudden transition by which we pass at once from the Silurian to the Devonian system, 

 either in fossils or in mineral matter: there are no disturbances, which could have broken 

 the general quiet of the period during which this great series was being deposited. At a 

 few points, inconsiderable movements may he observt d, affecting slightly a portion of the 

 deposit ; hut the same observation applies equally well to the Hamilton shales, and the 

 Helderherg division. The physical changes which seem to have occurred during these 

 periods, wore merely gentle oscillations, destitute of violence or rapidity. Hence these 

 rocks repose in unbroken strata ; or, if broken, the change of position amounts to a few 

 feet only ; or it is of such a nature as to have resulted in gentle flexures, along which the 

 layers remain unbroken. The mass has received, as a whole, that slight movement by 

 which the layers have been placed in a position inclining to the southwest at a very mode- 

 rate angle, a position "Which was given them when the great central primary mass north 

 of the Mohawk valley emerged from the Apalachian sea. 



§ 1. Portage and chemung groups of the genesee valley. 



The Moscow shales represent the Hamilton group in this valley. The rock is a light 

 gTeen, soft and fragile. A black date, interlaminated frequently with thin beds of black 

 limestone, succeeds the Hamilton shales both at Moscow and Geneseo. The change in the 

 mineral constitution of the rock is accompanied with a change also in fossils ; and, as has 

 been stated, microscopic orthoceratites abound in the layers which immediately succeed the 

 Moscow shales ; while, at the same time, all the characteristic fossils, without exception, 

 belonging to the last mentioned rock, remain below. Fossils, then, in this valley, and in 

 this series, determine where one group ends and another begins. We are not, however, 

 furnished with distinct lines of separation in the vicinity of the Catskill and Helderherg 

 ranges, as we shall have occasion to show in the sequel. 



