CRETACEOUS ERA. 143 



ferous trees (aUetites and strobolites), in drifted fragments, 

 are all or nearly all we can read intelligibly of the cretaceous 

 vegetation. And yet we know, from certain lignitic beds, 

 that considerable areas must have been clad with swamp 

 and forest-growth, and this during long periods of alternate 

 reproduction and decay."" On the whole, however, the cre- 

 taceous flora appears to have been by no means an exuberant 

 one less varied in its form than that of the oolite w r hich 

 preceded, and less southern in its aspect than that of the 

 early tertiary that followed. And the cause of this we find 

 in the colder currents of the northward opening seas seas 

 which occasionally brought drifting-ice even to the latitudes 

 of the British Islands if we are to seek in ice-floes, as Mr 

 Godwin- Austen has done, an explanation of the isolated 

 blocks of granite and lignite that have been recently found 

 imbedded in the chalk of the south of England. 



The marine fauna presents an exuberant display of sponge- 

 growth (spongia, ventriculites, siphonia, scyphia, &c.), all 

 less or more converted into flints j and leading to the in- 

 genious speculation of Dr Bowerbank, that their function 

 in nature is to induce the deposit of siliceous matter from 

 the waters of the ocean just as the corals assist in the con- 

 solidation of its calcareous constituents. Foraininiferous 

 organisms (textularia, rotalina, dentalina, lulima, &c.) in 

 countless myriads throng the waters, and drop their cal- 

 careous cases in such abundance, that more than the half of 

 some chalk strata is composed of their exuviae. It is now, 

 and during the dawn of the tertiary period, that foramini- 

 ferous life attains its meridian physiologically in hundreds 

 of generic forms, and numerically in such abundance that 



* Besides the cretaceous lignites of Europe, it is now known that the 

 coal of Vancouver's Island and other American localities "belongs to the 

 same epoch. It is also more than likely that some coal-fields, now sup- 

 posed to be oolitic, and several lignites now reputed of lower tertiary 

 age, will yet be found to belong to the chalk formation. 



