7t) [AsSEMBLT 



some forms of the Hamilton group. Many species of Avicijla 

 occur, and brachiopodous shells of the Genera Spirifer, Orthis, 

 Atrypa and Strophomena are abundant and beautiful. 



This group of strata contains many remains of plants : most 

 of them are very ill-preserved, but one quite perfect imprint of a 

 fern-like leaf is shown on Fig. 41. The original specimen was 

 found at Pine valley, Chemung county. 



The Chemung group passes or changes upward into the 



CATSKILL GKOUP, 



an enormous series of shaly and sandy strata, which cover all 

 the upper range of the Catskills, and many of the higher tracts 

 of the southern counties as far west as Steuben. In the latter 

 county it is only a thin mass of calcareous sandstone, and farther 

 west it thins out and disappears entirely ; but in the Catskill 

 region it is probably 2500 feet thick, and twice as much in Penn- 

 sylvania ; whence it is found southward along the mountain 

 ridges, but in thinner volume, as far as Tennessee. 



The beds of this series are various in color, being greenish 

 grey sandstones ; fine-grained reddish sandstones, slates and 

 shales ; grindstone grits, and an accretionary mass appearing like 

 fragments of hard slate cemented in calcareous rock. The hard 

 sandstone often weathers in a peculiar way, dividing into thin 

 layers almost like piles of boards. 



The fossils of this rock are very few : the shells figured (Fig. 

 42) were found by Prof. Yanuxem in a locality near Mount Upton 

 on the Unadilla. Remains of plants are numerous, forming occa- 

 sionally tiny seams of coal ; and there are in some localities 

 many teeth, bones and scales of fishes. The latter are often con- 

 spicuous objects, as they are usually white or bluish in color, 

 and contrast strongly with the red rock. A few specimens are 

 shown in Fig. 43. 



Above these " Catskill mountain strata," lies the rock which 

 is considered as the base of the great Carboniferous system of 

 Pennsylvania. It is mainly a mass of hard Conglomerate, 

 of rolled and rounded quartz pebbles cemented with sand 

 into a solid mass. Some of its finer or more sandy layers often 

 show a singular lamination in a diagonal or slanting direction. 

 It is remarkably massive and ponderous in its general appear- 

 ance, the ledges often separating into huge blocks with wide 



