380 "Prof. James Hall on the 



to the north and west of the we^ branch of the Delaware, and 

 to a great extent (if not entirely) the east and west branches of 

 the Delaware, there are no beds of rock of more recent age than 

 the Chemung ; and, from what I have seen elsewhere, I am in- 

 clined to believe that until we ascend the slopes of the CattsHU 

 mountains, and rise to an elevation of at least 2,000 feet above 

 tide-water, we find no rocks of newer age than the Chemung 

 group. 



The Cattskill group has been compared with strata newer than 

 the Chemung group, and consisting mainly of red and greenish 

 shales and shaly sandstones. I am now satisfied that the red shaly 

 sandstone near the base of the section, as here presented, has misr 

 led most of those who have heretofore investigated these rocks ; 

 while at the same time the harder and more arenaceous character 

 of the Hamilton rocks in their eastern extension (in which cha- 

 racter they simulate the Chemung rocks,) has caused them to be 

 identified with the latter. I am satisfied, moreover, that through 

 this means Mr. Vanuxem was misled ; and though I have not re- 

 examined the section at Mount Upton, the locality of the charac- 

 teristic bivalve shells, I am not willing to believe it will prove 

 to be newer than Chemung, even if it be much above the top of 

 the Hamilton. 



You will perceive, therefore, that all the specimens of plants sent 

 you as coming from the Cattskill group are really from beds of 

 the Chemung group proper ; and, so far as possible in this hastily 

 written note, I have given you my reasons for adopting this 

 belief. 



In looking back to the history of the adoption of the term 

 Cattskill group, it would appear that there was not entire unani- 

 mity as to its signification in some points, among the geologists 

 of the 1st, 3rd, and 4th districts. 



Prof. Mather, in adopting the term, says it includes Nos. 9, 10, 

 11, and 12 of the Pennsylvania Survey ; while Mr. Vanuxem 

 restricts it to No. 9. As both these gentlemen placed it above the 

 Chemung group as defined in central and western New York, I 

 regarded it (without having made personal examination) as iden- 

 tical with a red shaly sandstone and conglomerate which clearly 

 comes in above the Chemung in the adjacent counties of Penn- 

 sylvania bordering the 4th district. Having considered the Che- 

 mung group as No. 9 of the Pennsylvania Survey, I regarded the 

 red rock with Holoptychus as No. 11 ; the conglomerate. No. 10, 



