361 



increased, as far as the Jurassic formation is concemed, and to 

 have attained its maximum in the Great Oolite period. This I 

 believe to be due to the Coral sand, and, besides, to the 

 enormous increase of the calcareous encrusted vegetation of the 

 ancient seas, paralleled by what we can now observe in the 

 Carribean sea and Leeward isles, and if we need a further key to 

 the problem, we may observe a similar Oolitic formation, both as 

 to percentage of lime and roe-like structure being silently yet 

 surely constructed at the present day, in the seas of the Antilles. 



IV. PALEONTOLOGY. 



(1.) General. — The evidence aflForded by the palaeontology of 

 the Sfinatus Zone strongly bears out the statement of the last 

 paragraph, that we here possess an example of an old sea-bottom 

 of the mid-liassic epoch ; and also that we are justified in assign- 

 ing to it a definite position in the scale of depth. It formed a 

 shelving shore of the division, named by Professor Forbes the 

 Laminarian Zone, which would be about fifteen fathoms deep 

 from sea level. This position is shewn by two distinct but 

 associated groups of fossils. The first class of fossils would be the 

 marine vegetation. On carefully cleaving some of the more fissile 

 sands, and separating them along their planes of deposition, 

 the eye is presented with a varied surface strewn with elongated 

 cylindrical, but more often ovate stems, lying in disorder, either 

 branching from a main stem, of undefined length, or else 

 crossing and recrossing each other. Now, as these sands have 

 scarcely any plasticity, they yield but inferior casts of delicate 



objects. The impressions are, therefore, hard to interpret; 



and, from the absence of delicate markings, the knowledo-e 

 derived from them must of necessity be rather general than 

 specific in character. Beside the broader impressions or casts 

 and amongst them, occur undefined patches or blotches, orano-e- 

 coloured from ferric oxide, and resembling the laciniated fronds 

 of some cryptogamic plants. Their nature is tmquestionable. 

 They are the stems and other remains of algse of the olive-oroup, 

 which embraced the great sea-tangles. The stems are, where 



