AND OTHEK EOCKS IN CARBONIFEROUS LIMISIONE NFAR DUBLIN. 373 



existence of dry land is often confirmed (during the Carboniferous 

 period) independently, as in the case of the granite-sand and 

 fragments scattered in the carboniferous limestone of Dublin ; the 

 most probable cause for their occurrence being their transport in the 

 roots of plants, which grew somewhere on the granite laud, and were 

 washed down into the Carboniferous sea." 



Mr. Croll, in his 'Climate and Time' (p. 296), quotes the state- 

 ments by the first of the above authors in support of his argument 

 as to the existence of glacial conditions during the Carboniferous 

 Period. 



We have therefore two suggested theories as to the means by 

 which these fragments were transported and dropped in the sea at 

 depths sufficient for the growth of the organisms, such as Encrinites, 

 of which the limestone is composed. 



With regard to the former, I believe that all who carefully examine 

 the specimens now exhibited will agree that they exhibit none of the 

 indications of the existence of glacial conditions such as we might 

 reasonably expect to find. The fragments, so far as I know, are 

 invariably angular, and show no marks of having been acted upon 

 by ice, or even of having been rolled by water ; they look as if 

 they had been freshly broken or torn off the rocks from which they 

 were derived. Although some of them rest upon a thin earthy 

 parting in the limestone, their environment is strictly calcareous, 

 consisting largely of Encrinite-stems, and there is an absence of the 

 argillaceous silt which is so conspicuously present, for instance, in 

 the now well-known boulder-bed of the Talchir formation in India. 

 I am therefore unwilling to accept any iceberg or ice-raft theory of 

 transport, and would consequently reject the conclusions which have 

 been based upon that hypothesis. 



That the fragments of granite and other rocks now found in the 

 limestone were transported from their original sites by the agency 

 of plants, appears to be, upon the evidence, the only safe conclusion ; 

 but that these were terrestrial plants may I think be questioned, 

 though I cannot see that it can be actually disproved. To any one 

 who has examined the manner of growth of shrubs and trees on 

 poor rocks and soils, and has, moreover, noticed that, when over- 

 turned by storms or landslips, their roots often hold fragments of 

 rock firmly in their grasp, it may appear that the carrying out to sea 

 of such shrubs and trees by floods would afford a sufficient means of 

 explaining the phenomenon, especially as we have evidence of the 

 great distances to which fragments of stone have been borne by this 

 very agency. Still there is another possible means, and, as I venture 

 to believe, a more probable means, to account for the transport ; and 

 that is, that the fragments were conveyed into the deep sea, possibly 

 from no great distance, by means of seaweed, which during storms 

 had been torn from a submarine reef consisting of the rocks whose 

 fragments we now find imbedded. 



It is only necessary to traverse any sea-coast near to which there 



