BLAKE I EAST YORKSHIRE. 
29 
districts, the great deposits of boulder clay do not reach a 
height of more than 350 feet, and valleys above that elevation 
are free from it; but those below that depth were utterly 
obliterated by it. In some instances the new valleys run in 
the same lines as the old, but often the old valleys are still 
blocked up, and new ones run by their side or across them. 
Sometimes a double valley is formed on the two sides of the 
old one, leaving a long tongue of glacial material between. 
In the area of the chalk the phenomena are somewhat differ- 
ent, for the floating ice seems here and there to have caught 
the surface and torn it up and contorted it in a wonderful 
manner, while the relics of remote strata brought by the 
ice are left at higher elevations, and have a rather different 
character from the usual boulder clay, and appear to have been 
largely derived from the Lias, both on account of their 
mineralogical character and contained fossils. Into the 
formation of the several beds which constitute the Holder- 
ness, or the various deposits which stud the vale of York 
and bury its Triassic basis beneath 50 to 100 feet of superficial 
accumulations, some with the relics of mammals, some 
collected in the wildest confusion, and some tranquilly 
reposing clays or soft sands with remains of forest growth, I 
will not now enter, as I feel that there are others who are much 
more competent to deal with these matters than myself ; but 
must content myself with the above brief outline of those 
geological changes which have made East Yorkshire what it 
is, and have brought into existence those rocks on which the 
glacial agents have acted, and given their final touches to the 
scenes. 
