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initiations, known as beds of gravel, boulder clay, &c., are 
of varying character and nature, and also derived from 
different sources. They are, further, either extensive in 
their distribution, or limited and local. 
The Rev. Wm. Thorp, in an able paper read before this 
Society, has demonstrated four such gravel beds as occurring 
in Yorkshire, of different geological ages and derived from 
different sources, each possessing peculiar and well marked 
characters. The first of these, which covers vast dis- 
tricts in other counties, and is known as the Great Northern 
Drift, has transported boulders of rocks from Cumber- 
land and Westmoreland for 110 miles, over the plains of 
York, from the Tees to the Humber, and up to Flam- 
borough Head. The second is a range of gravel which 
touches the former, and varies from one to two miles in 
breadth, and passes down the rivers Aire and Calder, from 
Leeds by Ferrybridge, to Goole, consisting of pebbles derived 
from an entirely different series of rocks, — those of the coal 
formation, consisting of the carboniferous sandstone, and, 
occasionally, mountain and magnesian limestone, which 
proves the direction of the currents to have been from 
west to east. The third is a range which has an east and 
west course down the river Don, to the south bank of the 
Humber, the pebbles of which are also derived from the coal 
formation, but of the harder sandstone rocks of Rotherham, 
and the mountain limestone of Derbyshire. A fourth range 
of diluvium is that which extends from near Bawtry, to one 
of the highest points in Nottinghamshire, and is composed 
exclusively of magnesian limestone pebbles. Hence, while 
the former and most extensive, which consists of boulders 
of granite, &c, is supposed to have been the result of a 
great current from the north, these smaller, almost wholly 
composed of the rocks of the coal district or its neighbour- 
hood, are conjectured to have been derived from the 
