CHAPTER VI. 



THE LONDON CLAY — CONDITIONS OF ITS FORMATION. 



Of our children who pick up shells on the sea-shore and bring 

 them home to Hampstead as trophies of their, to them, great 

 but delightful travels and adventures, how few there are who 

 know that sea shells are in the clay on which their homes are 

 built. But the Hampstead shells are like those they only see 

 in the sea-side shop, and cannot find with all their industrious 

 search on the beach below, for they are similar to the beautiful 

 West Indian shells so temptingly displayed for sale, and thus 

 these shells teach the interesting fact that warm climatal condi- 

 tions prevailed during the formation of the clay of Hampstead, 

 for living volutes and nautili we know are only to be found in 

 tropical or sub-tropical seas. This conclusion is confirmed by 

 the remarkable fossils of the Isle of Sheppey. The many 

 remains of turtles there found, together with the abundance of 

 fossil tropical-like fruits have led some to the conclusion that 

 torrid conditions obtained, but the small size of the volutes and 

 other warm sea shells seem to indicate rather a moderately 

 warm or sub-tropical sea, but certainly one much warmer than 

 that which now washes the shores of the British Islands. 

 Although not a very deep sea, there is reason for supposing 

 it to have had a depth that would allow of a considerable 

 variation of temperature, and have much warmer water where 

 shallow near the shore than at its greater depths, by which 



