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INTRODUCTION. 



Having mastered the characters of the rocks, by 

 passing from specimen to specimen with the index in 

 his hand, the student will be able to form as fair an 

 idea as can be gathered in a museum of the lithological 

 or stony structure of most of the British formations in 

 their order of succession, 

 land and Wales the tertiary rocks 



ravel, sand, and clay, with a little soft limestone 



He will find that in En^- 



are mostly formed 



of 



con- 



the secondary rocks, of chalk, clay, soft shale, o 

 and hydraulic limestones, marls, sands, and 

 glomerates ; the carboniferous rocks, of harder shales, 

 ironstones, sandstones, fireclays, beds of coal, and hard 

 limestone ; the old red sandstone chiefly of red marl 

 sandstone, and conglomerate ; and the Silurian and 

 Cambrian rocks in great part of mudstones, grits, and 

 slaty rocks, with occasional shales, limestones, and 

 beds of conglomerate and sandstone. Such is the 

 general nature of the rocks in England and Wales ; 

 but in other parts of the world there are local pecu- 

 liarities, which can be easily understood in reading 

 special works after the student has studied the rocks 

 of his own region. 



The names of the places from which the specimens 

 were taken are always mentioned, thus securing in some 

 degree the advantages of a topographical collection. 



Excepting the foreign specimens necessary for illus- 

 tration, almost all the specimens were collected during 

 the progress of the Geological Survey previous to 1856, 

 and partly serve as type specimens illustrative of the 

 maps and districts surveyed up to this date. 



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