80 LITHOLOGICAL GEOLOGY. 



resting on the shale. Above this (5) is another greenish shale, 

 much like that below. Then (6) is another great stratum of lime- 

 stone ; 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, more- 

 over, each may be traced for a great distance through the adjoining 

 country. 



Throughout far the larger part of America, as well as all the other 

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

 of almost universal distribution. They make up the mass 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 in 

 the Connecticut valley. They are the prevailing rocks of Britain, 

 including within their series the chalk, oolite, coal strata, and others. 

 They occur over nearly all Europe, spread throughout the great 

 plains of Russia, through Asia nearly to the tops of the Himalayas, 

 over South America to some of the summits of the Andes, and 

 through Africa and Australia. These stratified rocks are in striking 

 contrast with the unstratified, — granyte, for example, which may 

 show no appearance of layers even through heights of a thousand feet 

 or more. Many volcanic masses of rock are unstratified. Yet the 

 volcanic mountain has usually a stratified arrangement, successive 

 layers of lava and volcanic sand or earth being piled up to make the 

 cone. Even among crystalline rocks, the distinction of strata may 

 often be made out, although much disguised by changes in the course 

 of their history, 



The succession of strata in stratified rocks is exceedingly various. 

 In the section given, there are alternations of limestones, shales, and 

 sandstone. In others, as at Trenton Falls, N. Y., there are only lime- 

 stones in sight ; but, were the rocks in view to a much greater depth, 

 sandstone strata would be seen. In still other regions, there are al- 

 ternations of conglomerates and shales ; or conglomerates with shales 

 and coal-beds ; or conglomerates with limestones and sandstones ; or 

 shales and sandstones alone. 



The thickness of each stratum also varies much, being but a few 

 feet in some cases, and hundreds of feet in others ; and the same 

 stratum may change in a few miles from 100 feet to 10, or disappear 

 altogether. In the Coal-formation of Nova Scotia there are 15,000 

 feet of stratified beds, consisting of a series of strata mainly sand- 

 stones, shales, and conglomerates, with some beds of coal ; and in the 

 Coal-formation of Pennsylvania there are 6,000 to 7,000 feet of similar 

 character. 



