Introduction to Geology. 69 
** Deposits originating in the way we have described must 
necessarily be of variable thickness, and liable to every possible 
modification from the action of mere local causes. Any useful 
classification of their component beds would, perhaps, never 
have been effected, had not the organic remains, preserved in 
them, exhibited an extraordinary Eo mity of character and 
arrangement. An accurate examination of these spoils has, 
ther efor e, supplied us with the means of establishing analogies 
between phenomena which otherwise must have appear edt en- 
tirely unconnected.” 
These deposits seldom appear consolidated in the form of 
rocks, but generally consist of varieties of clay, marl, and 
sand, with occasional concretionary masses. In this section 
also occur two or three alternations of fresh-water or lacustrine 
beds; that is, of deposits, which, from the numerous shells 
they contain, resembling the Testacea of lakes and rivers, are 
judged to have originated i in fresh water. In Bavaria they are 
stated to contain perfect beds of coal and iron-stone. In France 
this class seems to have been carried, somewhat higher than 
in the English series. The latter comprises the plastic clay 
and its accompanying sands, the London clay, the upper 
marine or mixed fomnstion of the Isle of Wight interposed 
between the fresh-water strata, the shelly crag ce Suffolk and 
Norfolk ; and, above all these, particularly in fhe south-east and 
eastern counties, appears a vast irregular accumulation of 
debris, or water-worn and transported fragments of all the 
preceding formations, known by the name of diluvium. 
Dr. Buckland nome the remarkable occurrence of insu- 
lated portions of tertiary strata on the summits of the Savoy 
Alps, at elevations of more than 10,000 ft. above the level of 
the sea; and the observations of geologists have now fully de- 
termined the fact, that tertiary formations exist in every quarter 
of the globe, and differ in few essential respects from those 
in this country. 
ivi 
High Down. 
Headon Hille 
1 
London Sands and Clays, 
$ Clay. Plastic sertes. 
Hortzontal Strata, Vertycal Strata of Alum Bay, 
Isle of Hight. ) 
We have selected an illustrative section of the western ex- 
tremity of the Isle of Wight (fg. 17.), where the entire series 
F 3 
