GEOLOGY OF NORTH ATLANTIC GILLIGAN 221 



Taken altogether, Labrador seems a more promising area, as far 

 as the gneisses and foliated granites are concerned, from which 

 could have been derived the necessary types of minerals which have 

 been enumerated above as making up the sedimentary rocks of the 

 pre-Cambrian and Paleozoic systems round the North Atlantic. Of 

 the large suite of basic rocks and metamorphosed sedimentary rocks 

 given by Coleman, however, little or no trace is found in the sedi- 

 mentary rocks with which I am dealing, and for that reason it ap- 

 pears evident that Labrador, as far as is at present known, can not 

 be regarded as a land mass which would contribute almost exclusively 

 granite material. 



THE SIZE OP THE AREA 



The present-day Mississippi, with its tributaries, drains an area 

 the size of Europe with the exception of Russia, Norway, and 

 Sweden, and its delta covers an area of 12,300 square miles. The 

 delta is advancing about 262 feet per annum at the Passes, and the 

 amount of detritus brought down each year would build a prism 268 

 feet high on a base having an area of 1 square mile. The belt of 

 clastic deposits surrounding the North Atlantic and derived from 

 the ancient land mass would make up many such deltas as that of the 

 Mississippi, and correspondingly must the land mass from which 

 these were derived have exceeded that which has so far been laid 

 under contribution for the Mississippi Delta. Vertical as well as 

 horizontal dimensions must be considered; since if we regard as 

 reasonable that the major portion of the clastic material of each of 

 the named periods was derived at first hand from the parent rock, 

 then this necessitates the same area being subjected to denudation at 

 many successive periods, and this is easier to conceive of as due to 

 repeated elevations of the old lands. 



THE POSITION OF THE AREA 



The evidence which I have given of the distribution of the result- 

 ing sediments points conclusively to the land mass being situated 

 in what is now the North Atlantic region. Summing up all the 

 evidence, it appears to me convincing that the present land masses 

 surrounding the North Atlantic, even when brought together as has 

 been suggested by Wegener and others, could not give us all that 

 is required in the type and amount of sediment, and therefore either 

 these lands must themselves be much extended beyond their present 

 boundaries and these extended areas consist of different materials 

 from those which characterize the present fragments, or there was an 

 actual continental area occupying the whole of the present North 

 Atlantic which has since broken up and foundered. 



