188 CATSKILL DIVISION. 



Geologically this is an interesting part of the New-York series. It forms by itself a dis- 

 tinct system, and has been described by Mr. Phillips under the name of Devonian system. 

 It is designed to embrace not only the peculiar rocks of Devonshire, but those of Scotland, 

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

 name of Old Red sandstone. Comparing our rocks of this division, however, with what 

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

 serving, in this 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 remarkable forms ; but in no place in this country, where this 

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

 associated 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 tliis country, whatever diflferences 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 be observed, affecting slightly a portion of the 

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

 Helderl)erg division. The physical changes which seem to have occurred during these 

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

 rocks repose in lurbroken strata ; or, if broken, the change of position amoimts 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 

 green, soft and fragile. A black slate, 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 aliound 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 Helderberg 

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



