245 
also some very extensive tracts of surface over which no 
traces of general gravel beds, or of general transporting 
currents, can be found ; and these latter, (where no gravel 
beds are found,) require some investigation from the Geolo- 
gist as to the cause of the absence of transported material. 
I shall, therefore, shortly describe the three extensive 
tracts of gravel which cover great parts of Yorkshire and 
Nottinghamshire, and then offer some explanation of the 
absence of these deposits in the Yorkshire and Derbyshire 
Coal Fields. 
Commencing with the north parts of Yorkshire is one of 
the largest and best known dispersions of boulders and gravel 
which Great Britain presents. These fragments, which 
consist of rocks now existing " in situ," in Cumberland, are 
dispersed, first on the west side of the chain of hills which 
separate Yorkshire from Lancashire as far south as the river 
Severn, i.e. by Castle Eden, Preston, Lancaster, Manchester, 
the valley of the Trent, over the plains of Cheshire, Staf- 
fordshire, and through and over extensive districts in Wales ; 
but here there are certain exempted localities, which afford 
some clue to the causes which have likewise exempted certain 
places in Yorkshire, Derbyshire, and Nottinghamshire, from 
this deposit ; and it is remarkable that no incursion of these 
boulders has been made over the chain of hills to the east, 
but the Penine chain has acted as a natural dam against 
them. 
On the east side of the Penine chain, the Cumberland 
boulders cover the plain of York from the Tees to the Hum- 
ber. Then, again, masses of granite from Shap Fells, (recog- 
nised even in hand specimens by any Geologist who has once 
seen this rock,) have passed over Stainmoor Forest, 1,400 feet 
above the sea, thence over the Oolite hills, 1,500 feet, down 
to the East coast, where the united thickness of the upper 
and lower beds of erratics is between 300 and 400 feet. 
