22 
BLAKE : EAST YORKSHIRE. 
the south. Accumulations of oolite, reaching in Biccaldale 
as much as 150 ft., were derived from this source, though the 
homes of the corals themselves are swept away. An inunda- 
tion of sand, however, once more interfered with its tranquil 
formation, and, as the middle calcareous grit, separated one 
coral growth from another. Then came the coralline oolite, 
still derived from localities now unknown. From their 
thickening, however, towards the centre of the Pickering 
valley, we may conclude that the coral reefs themselves stood 
somewhere within the confines of that valley ; and this is 
rendered more probable as it is round its edges that we find 
them still left in situ where they spread outwards and 
covered the old deposits. The luxuriousness of their growth 
was marvellous ; and the profusion of life which accompanied 
them, or dwelt in snug nooks in their neighbourhood — such 
as where North Grimston now is — was not far from equal to 
that of the tropics of to-day. In this area undoubtedly 
flourished the finest coral reefs that England has ever seen 
since the period of the Oolites of Bath, 
Curious changes have passed upon some of these rocks since 
then, the origin of which is difficult to account for. Instead 
of their original calcareous material, an enormous amount of 
silex has been introduced, turning an oolite into a silicious 
rock in some places, developing great flints in others. The 
calcareous matter of the middle grits has in like manner been 
totally extracted, leaving but a skeleton of sand behind. 
These changes have taken place to so complete an extent, that 
were the silex removed, scarcely any rock would now be left. 
Hence the infiltrating mineral could not have come from the 
rock itself ; and however we may try to explain the origin of 
flint in chalk by means of the sponge specules, and other 
silicious bodies it originally contained, some other method of 
interpretation must be adopted here. But to continue the 
history. 
