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more powerful current, and that the sand was afterwards 
deposited over it, but in very many cases the above is 
certainly the true explanation. Although the larger rounded 
pebbles have a great tendency to roll to the bottom of the 
slope, some of more irregular form or those accidentally 
entangled in the sand have sometimes remained higher up, 
scattered amongst the sand, yet often in bands, probably 
indicating some variation in the velocity of the current. 
All these peculiarities in the arrangement of the materials 
had been explained by my experiments on the angles of rest 
of various deposits, but since then I have been able to still 
further prove the truth of my deductions by means of my 
machine for producing drift-bedding artificially, described 
at the meeting of the British Association at Cheltenham, 
(Report for 1856, p. 77); and in my Paper on the Tertiary 
Estuary of the Isle of Wight, (Ed. New Phil. Jour., n.s., 
vol. v., p. 280). If coarse emery be mixed with fine white 
sand, it is arranged along with the sand, when they are 
deposited by the action of the machine precisely in the 
manner I have described ; the artificially prepared deposit 
being in all respects analogous to the naturally formed 
millstone-grit, the resemblance being so close that I was 
even led to perceive some very important peculiarities in 
the natural rock by examining what took place in the 
formation of the artificial deposit. 
By far the greater part of the pebbles in the millstone- 
grit in South Yorkshire are of white quartz, but only a 
very moderate amount of examination will enable any one 
to see that pebbles of felspar are not at all uncommon. 
These are now often very much decomposed, though some 
are not, but are semi-transparent and have a clear sharp 
cleavage. If the sandstone itself be carefully examined, it 
may be seen that it is composed of the self-same materials 
as the pebbles, in a finer state of division ; but the felspar 
