

CHAPTER XX 
GEOLOGICAL SURVEYING—continued 
Mapping of Unconsolidated Tertiary Deposits, and of Glacial and 
Fluvio-glacial Accumulations—Boulder-clay ; Roches Moutonnées ; 
Terminal Moraines, etc. Raised Beaches. Lacustrine and Fluvia- 
tile Deposits. Peat. 
Superficial Accumulations.—In this and other countries 
the “solid” rocks are often concealed under sheets of uncon- 
solidated materials, as gravel, sand, loam, clay, etc. Some- 
times these superficial accumulations are confined to valleys 
and depressions, or they may mantle the entire surface of 
broad, low-lying lands. They are of very various origin— 
marine, fluviatile, lacustrine, terrestrial—some dating back to 
early Tertiary times, while others belong to later periods, and 
many are still in process of formation. 
The TERTIARY deposits of this country, owing to their 
generally unconsolidated condition, their inconsiderable thick- 
ness, and limited extent, may be looked upon as “superficial 
accumulations.” They are chiefly marine, and practically 
confined to circumscribed areas in the south-east and south 
of England. On the continent, however, they cover much 
more extensive areas—in some of which the deposits are 
essentially of marine origin, while in other regions they are 
freshwater, or may consist of an alternation of marine and 
freshwater accumulations. In North Germany, Belgium, 
France, and England, the beds are arranged in approximately 
horizontal positions—the marine and fluvio-marine deposits 
occurring for the most part in maritime districts, and seldom 
reaching more than a few hundred feet above the sea. The 
deposits vary much in character—in some places consisting 
largely a clay or marl, in other places of sand or gravel. 
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