OOLITIC ERA. 129 



ical conditions extremely different from those of the trias, 

 and apparently more favourable to an exuberant exhibition 

 of vitality. In its ascending series of Lias, Oolite, and 

 Wealden, we have a succession of deep-sea, littoral, and 

 estuarine deposits, which, in the old world at least, spread 

 over wider areas, and are in their calcareous muds, clays, and 

 limestones, much more conservative of organic structure. 

 Xot only do the seas show broader and more southerly ex- 

 panses, but they are more connected, and seem to have been 

 less liable to sudden variation either in their depth or con- 

 figuration. Their waters were likewise more normal in 

 their composition, and we get quit of those super-saline 

 and ferruginous constituents which, in the trias, appear to 

 have been as unfavourable to the development as to the 

 preservation of organic nature. The land also assumes a 

 more continental aspect, and, under a genial climate, gigan- 

 tic rivers and estuaries bespeak conditions conducive alike 

 to numerical abundance and specific variety. In conjunc- 

 tion with these new conditions of area and climate, vitality 

 puts on newer aspects. The palaeozoic forms that lingered 

 in the trias altogether disappear, and mesozoic life, in a 

 prolific flora and fauna, attains its meridian of development. 

 In vegetation, palms, lilies, and other allied monocotyledons 

 are on the increase ; tree-ferns, cycads, and conifers, are the 

 dominant orders; while dicotyledonous types make their 

 appearance in fragments of wood, leaves, and inflorescence. 

 In the animal kingdom the advance is still more marked 

 and decisive. Zoophytes and other lowly orders are more 

 abundantly and beautifully preserved; sea-urchins, star- 

 fish, and crustaceans assume generic aspects more akin to 

 existing races ; bivalves and gasteropods are still largely on 

 the increase, and cephalopods attain their specific and num- 

 erical meridian ; the fishes more closely approximate the 

 existing ichthyic type ; and though indications of mammalian 



