90 LITHOLOGICAL GEOLOGY. 



II. CONDITION, STRUCTURE, AND ARRANGEMENT 

 OF ROCK-MASSES. 



96. The rock-masses of the globe, or terrains, as they are called, 

 occur under three conditions: (1) the stratified, (2) the unstratified, 

 and (3) the vein condition. Under each there are different pecu- 

 liarities Of STRUCTURE and Of ARRANGEMENT. 



1. STRATIFIED CONDITION. 



Under this head the subjects for consideration are: — 1. The na- 

 ture of stratification ; 2. The structure of layers ; 3. The positions 

 of strata, — both their natural positions and dislocations ; 4. The 

 general arrangement of strata, or their chronological order. 



1. Nature of Stratification. 



97. Stratified rocks are those which are made up of a series 

 of layers or strata. The annexed sketch represents a section 

 of the strata as exhibited along 



Genesee River, at the falls near s * 



Rochester. The whole height of 

 the section is 400 feet. At bottom 

 there is a thick stratum of sand- 

 stone (1) ; next above it lies a hard, 

 gray layer (2), which has been 

 called the Gray Band. Upon this 



rests (3) a thick bed of greenish shale, a fragile, imperfectly 

 slaty rock. Next (4) is a compact limestone forming a wide- 

 spread stratum resting on the shale. Above this (5) is another 

 greenish shale, much like that below. Then (6) is another great 

 stratum of limestone; then (7) another thick bed of shale; and, 

 finally (8), at the top is a limestone wholly different from those 

 below. The transition from one stratum to another is quite 

 abrupt, and, moreover, each may be traced for a great distance 

 through the adjoining country. 



Throughout far the larger part of America and all the other con- 

 tinents the rocks lie similarly in layers, so that stratified rocks are 

 of almost universal distribution. They make up the most of the 

 Appalachians ; cover nearly all of New York ; underlie the great 

 plains of the Ohio and Mississippi; occur over the larger part of 

 the slopes and summit of the Rocky Mountains, along much of the 

 Pacific border, as well as the Atlantic ; and exist as red sandstone 



