102 



GEOLOGY OF THE SECOND DISTRICT. 



in the grouping proposed ; while it leaves us at leisure to subdivide, if necessary, and study 

 the several groups as minutely as we please, or as the nature of the formations require. 



CHAMPLAIN GROUP. 



Some of its most important characters. — The order of succession, or the superposition of 



the members composing it. 



Returning now to the consideration of the members of the Champlain group, I shall pre- 

 sent, in the first place, a section giving the names and the order of succession of the rocks 

 composing it. 



Priihitii^. 



Chanip^aia Group, fir Lower Tratisition Rocks. 



1. Primary ; 



2. Oxidea of iron ; 



3. Potsdam sandstone ; 



4. Calciferous sandrock ; 



5 Chazy limestone ; 



6. Birdseye limestone ; 



7. Trenton limestone ; 



8. IHica slate ; 



9. Lorrain shales ; 



10. Grey sandstone ; 



11, Medina sandstone. 



1. Potsdam Sandstone. 



Disturbances. — Fossils. — The base of the Transition System. — Diversity of materials. 



The base of the Transition system of New- York is the Potsdam sandstone. Its lowest 

 portion is a granitic conglomerate, in which large masses of quartz, the size of a peck mea- 

 sure, are often enveloped : they are rounded and water-worn, and held together merely by a 

 finer variety of the same materials. The part which is properly a standstone, presents some 

 variety of aspect and texture at the different places where it appears ; but there are two prin- 

 cipal varieties, which it may be well to notice : ] st, an even-bedded and somewhat porous 

 rock, at many places a distinct white friable sandstone ; in others, it is a yellowish brown 

 sandstone, the particles of which are compacted together, so as to form a firm even-grained 

 mass. The rock at the Potsdam quarry furnishes a good variety of the latter ; those of 

 Bangor and Moore, of the former. 2d, a close-grained, sharp-edged mass, with natural joints 

 traversing it in two principal directions, so as to divide it into acute rhomboids, so closely 

 wedged together that it is with difficulty quarried. It is, in fact, a hard quartz rock, scarcely 

 passing for a sandstone. Keeseville, Whitehall and Port Kent furnish examples of this 



