***** 



. brln g tn 



,tel y abo* 

 of Sodi 



STEATIFIED ROCKS. 



39 



sandstones (Roth 



of England and Ger 



1852.) 



and those 



a tes. 

 not been i 



ts 



> 



have 



jpecUDW 



ae 



•on 



■: 



1' 



the 



4 



in 



sbeen 



d the 

 thers 



ft 



o 



;.ll <P 



illltf 



1 am 



o4 





f the - t 



P<fj 



r o< 





tlie 



1 or 



pet' 



many, there are sometimes blocks of several feet in diameter, 

 and from conglomerates of this degree of coarseness every 

 gradation may be traced, until at length they pass imper- 

 ceptably into grits and sandstones, (see Nos. 45 to 51,) from 

 these into marls, shales, and clays (see Nos. 127 to 146). 



Upper 

 Gallery. 



Wall-case 4: 



Q. F h TrU ° Cla ^ S are necessaril 7 more or less aluminous, but in 



*' _r\ 4- Ir% f\ -*% — j% _*% ^>*«^_ rf-k. ^ _i- *■%_ _1_ I-. .__ _T1 _ fiTV ______ I TIT -«, 



other respects the difference between shales, sandstones, 

 and conglomerates lies merely in the fineness of the grain. 

 An examination of many sandstones with the magnifying 

 glass, shows that their component grains are more or less 

 rounded by attrition in water, like the pebbles of the con- 

 glomerates Nos. 14, 15, and 19. This naturally leads to 



11 varieties the subject of the mode of formation of stratified rocks in 



70 chief var general. 



nents are Stratified rocks are of two kinds, chemical and mechanical. 



Wall 



forming ^ea of the manner by which stratified rocks are chemically 



j n | deposited. Without 



entering 



into details, those formed 



mechanically are chiefly deposited in lakes, and in the sea, 

 ed in a I in the slia P e of sediment. All rivers carry sediment to 

 t that fe the Sea ' ^ tlie disintegration and waste of the land through 



which they pass. Manj 

 by the action of breakers, and this is the chief cause 

 of irregularities in the outlines of shores. The sediment 

 thus formed is spread abroad in the sea to form strata. 

 Sea-weed, shell-fish, and other organic bodies, live and die 

 among it, and as the successive beds accumulate, they 

 frequently consolidate, and the whole becomes petrified or 

 turned into stone, partly by pressure, partly by chemical 

 actions. In this manner fossils become embedded and 

 preserved in rocks ; in this manner also, sediments are 

 being formed of every degree of fineness. There are gra- 

 velly beds on the beach, and by movements in the water 

 and the slope of the ground pebbles are, by degiees, carried 

 along the sea bottom many miles from shore. Other strata 

 are formed exclusively of sand, some of mud or clay, others 



