252 
Then, again, respecting the three or four ranges of east 
and west gravel derived from rocks now in situ, within fifteen 
to thirty miles of the drifted material, there can be no doubt 
that they have been exported from within the Yorkshire coal 
field, by the waters which were driven eastward during the 
time of emergence (mentioned by Trimmer), and down the lines 
of valleys which then formed the easiest retreat for the retiring 
waters. It is true that from organic remains in these coun- 
ties, we have few proofs of submergence; yet one good one is 
worth a hundred in such a case, and there are now in Lady 
Milton's possession two shells found in the gravel of Notts, 
near Osberton, about sixty feet above the sea, which have 
been identified by Professor Edward Forbes as species of 
those now living in the German Ocean ; and my friend, Mr. 
Denny, is now exhuming, from a brick field in the neighbour- 
hood of Leeds, the remains of one or two specimens of the 
great northern hippopotamus. 
Hence it is evident that there exist over this tract of 
country various deposits of gravel derived from very different 
sources, — each, however, significant of its origin ; while there 
are also localities containing scarcely a single pebble, whose 
plains have been protected by the high bluff lands of the 
North of Yorkshire. 
