Rocky Mountains. 435 



emerging from beneath the sandstone, which forms the body 

 of these mountains at M'Connel's Town, and in most of the 

 vallies between the Alleghanies. We learn from Maclurc, 

 that it extends to the south and west nearly to the termina- 

 tion of this range of mountains at the confluence of the Ala- 

 bama and Tombigbee rivers in Mississippi. 



Ill, — Transition ArgillitC' 



This name is intended to comprehend not only the com- 

 mon varieties of the clay slate with inclined laminae, but also 

 some varieties of gray wacke, and the silicious slate, by some 

 considered a distinct stratum. It is believed that throughout 

 the range of country occupied by the several rocks here men- 

 tioned, they will be found too intimately blended, and too 

 closely entangled with each other to allow of their being con- 

 sidered as separate formations. 



Geographical Distribution. — The formation including the 

 abovementioned rocks has been denominated clay slate. As 

 far as our acquaintance has extended, it occurs in all its locali- 

 ties associated with metalliferous limestone, or old red sand- 

 stone. It is not to be confounded with the primitive argillite 

 which occurs below transition limestone, and is met with in 

 the highly primitive parts of New England, nor with the 

 aluminous schist of the great secondary formation to the west. 

 It is distinct from either, and in most instances its character 

 is sufficiently marked. It occurs in the central portions of 

 that extensive strip of transition which skirts the western 

 margin of the primitive of New York and New England, and 

 forms the great body of the Alleghany and Catskill Moun- 

 tains. It is wider and more extensive in the north, occupy- 

 ing much of the surface in Vermont, the northern parts of 

 the state of New York and Canada. In the Alleghany Moun- 

 tains of Pennsylvania, Maryland, and Virginia, its beds are 

 of great thickness, and form in some instances, the prevailmg 

 rock, being, however almost invariably overlaid by sandstone. 

 It has in several instances been observed to contain impres- 

 sions of organized beings, but these are usually those of 

 zoophytic animals, and are exceedingly unlike those found so 

 abundantly in the schist of coal formations. Its colours are 

 variable, it is, however, most commonly bluish-black or 

 dark brown. Between Albany and Pittsfteld, it is met with 

 of a green colour, and a few miles to the southeast of White- 

 hall, New York, it is bright red. 



