60 



Into the sea, but were either completely rotted or were accumu- 

 lated under favourable conditions near shores at some distance 

 from Dorset. It is, however, conceivable that vast accumulations 

 of the decaying waste of extensive mats of seaweed floating at 

 the surface, like the Sargasso weed of the present day, may have 

 gradually settled down on the floor of the sea and there, mixed 

 with the fine inorganic s : lt, have undergone some slight further 

 decay before being finally locked up and consolidated as bituminous 

 shale. 



Another possible source, of the bitumen has been suggested in 

 the coal measures, which were possibly extensively exposed to 

 denudation over Britain and to the south-east over Belgium and 

 France, in the land surface of the Kimmeridgian period. Just as 

 the dark and sombre clays, shales and slates of the carboniferous 

 and earlier systems may have contributed largely to the accumu = 

 lation of the clays which form by far the greater mass of the Kim- 

 meridge formation in England, the seams of coal may have pro- 

 vided, after ultimate disintegration, the carbonaceous material out 

 of which the bituminous oil-shales were accumulated. No recog- 

 nisable fragments of ordinary Coal-Measure coal have, however, 

 been yet recognised in the oil-shale, which is indeed usually leather 

 brown and not grey or black. 



Though the Kimmeridge sea was shallow and contained no 

 great volume of water and became heavily charged with mud 

 from its land borders, it was yet fairly extensive, both in width 

 and length. It is, of course, possible that with : n the depths of 

 such an extensive sea, not only the varied vegetable waste, but 

 also the coal fragments carried down bv the rivers into the sea 

 were reduced by maceration and partial decay to a richly organic 

 mud, and that this was slowly deposited at certain stages in the 

 quieter waters of the vast but shallow Mediterranean Sea. In 

 such a manner an amorphous orgairc ooze of the sapropel type is 

 being laid down at the present time in freshwater tarns and lakes 

 In this and other countries. Such a mud. on consolidation, yields « 

 a brown regularly-foliated shaley peat, which yields hydrocarbons 

 on distillation and burns with a bright luminous flame. 



In the case of Kimmeridge Clay it is, however, not necessary 

 to go far to find a likely source for the carbonaceous material 

 enclosed within it. The formation is very rich in animal fossils, 

 and is remarkable, not so much for the number of species repre- 

 sented, though the range of forms is very wide, as for the vast 

 number of individuals enclosed in its strata. The sea must simply 

 have teemed with life of everv kind. In addition to various fora = 

 men if era and gasteropods and lamellibranchs of the shallow and 

 fairly deep waters, there lived a large number of cephalopods, 

 represented by the ammonites and belemnites — some of gigantic 

 size. But the most striking fossils are the remains of the great 

 reptiles of various tvpes. Thev abounded nt that tinv*, donvnating 

 the waters, the land and the air in a way that no other single class 

 "has ever done. Lizard-like reptiles, the Plesiosaurians, inhabited 



