Rocky Mountains. 433 



northeast, to the confluence of the Alabama, and Tombigbee, 

 in the southwest. An outline of the geological features of this 

 great chain has already been traced by Maclure, and parti- 

 cular accounts of portions of it are to be found in the works 

 of Eaton and others, we shall therefore confine our attention 

 to those strata, which, forming the northwestern side of the 

 range are most intimately connected with the great secondary 

 formations of the west. 



I. — Granular Limestone 



Appears in every part of the United States, where it has 

 hitherto been observed to be the uppermost in the series of 

 primitive rocks. It is true, it is often found to graduate by 

 minute and imperceptible shades of difference, into that 

 which is decidedly secondary. Instances of this have been 

 observed so frequently that the fact can be no longer ques- 

 tioned. This fact, and others of the same kind ought not 

 perhaps to be considered as invalidating the received opinions 

 with regard to the classification of rocks according to the 

 doctrines of Werner. If a division is to be made of the rocky 

 strata of the earth into primitive, transition, &c. it is perhaps of 

 little importance whether the boundaries tlius instituted, shall 

 traverse beds of the same substance, or separate contiguous 

 strata composed of different materials. 



That series of rocks next in order to the primitive lime- 

 stone abovementioned, has been very generally denominated 

 the transition class. It comprehends the following strata, 

 metalliferous limestone^ clay slate ^graywacke^ and graywacke- 

 slate^ and old red sandstone. If we confine our attention to 

 the consideration of these rocks as they exist in our own 

 country, we shall find them appearing in their different lo- 

 calities under circumstances of considerable uniformity. 



II. — Metalliferous Limes to?ie. 



The prevailing colour of this rock is blue of various shades 

 and intensities, varying into yellow and gray. It has usually 

 a close texture, an even, large choncoidal, or somewhat 

 splintery fracture. In many varieties, the surface by long 

 exposure becomes coated with an incrustation of a yellow- 

 ish-white powdery matter, which adheres closely. It is fre- 

 quently traversed by small recticulating veins of quartz or 

 calcareous spar, which during the gradual decomposition of 

 detached masses, resist the progress of disintegration, and 

 are left standing out from the surface, giving it a chequered 



VOL. II. 55 



