PALEONTOLOGY OF NEW-YORK. 
52 
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We are yet unprepared to speak with the same degree of certainty 
regarding the source or direction of the materials constituting the Cats- 
kill mountain group. If, however, these have been the same as in the 
preceding sedimentary strata, the force of the current which accumu¬ 
lated the sediment so abundantly along the eastern part of New-York, 
and spread it to near the western limits of the State, has been too weak 
to extend the same over the west, corresponding to the zone of the 
sediments immediately preceding this epoch. We have, therefore, no 
means of demonstrating by actual continuity of formation, that the 
epoch of the Catskill group was marked by sedimentary strata in the 
west. 
Directing our observations along the line of the Appalachian chain, 
we find, succeeding to the coarse conglomerate of the summit of the 
Catskill mountains, a formation of red shale with calcareous bands, 
which, in Pennsylvania, attains a thickness of three thousand feet, 
and is succeeded by the conglomerate of the Coal measures. What¬ 
ever may have been the source of this deposit, or the course of the 
current which transported the material, the formation itself has a 
very limited westerly extent, and is not known in the Western States. 
Its precise relations, moreover, to the rocks of the west are not deter¬ 
mined, as we shall see farther on, and its fossils are essentially 
unknown. 
At this point in our study of the strata, we should notice a fact of 
great importance, both in regard to the sequence of formations, and as 
influencing any general conclusions we may be inclined to draw. We 
have seen that the series in the west, from the Upper Helderberg 
group to the Chemung group, is identical in New-York and in the 
Mississippi valley. From that time to the commencement of the Coal 
measures, the sequence in the east and west is very different. 
The following table of formations will explain their order in the two 
districts of the country : 
