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 peculiarities 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 



Grenesee River, at the falls near Flg * 60 ' 



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 



