296 SCOTT'S LAST EXPEDITION 



rocks of Western Australia, or Eastern Canada that is, they 

 are of pre-Cambrian age. They were laid down for the most 

 part by the agency of water, the schists and limestones being clays 

 and chalks when they were formed. The sea-bottom on which 

 these deposits collected was subject to continual up-and-down 

 movements, changing the character of the deposit, for we find 

 in rapid succession and in thin layers schists which were fine muds, 

 next to quartzites which were sandbeds, and marbles which were 

 either deep-water chalk deposits or shallow clear-water coral 

 reefs. 



On account of the complex folding of these beds, as well as 

 the difficulty of obtaining a measurable section, we are unable 

 to make any definite statement as to their thickness, but they can- 

 not have been less than 15,000 to 20,000 feet. But figures are 

 of little value, since there is no method of ascertaining what thick- 

 ness of strata has since been denuded from the surface. The 

 folding and heating of the rocks has since quite destroyed all 

 evidence of the animal or vegetable life of that time, though 

 numbers of small graphite particles, found in the crystalline lime- 

 stones, may be the remnants of carbonaceous growth in the an- 

 cient coral reef. 



Our earliest view, therefore, of the region is that of a sea 

 bordered by land long since used up in forming these deposits 

 of mud, sand, and limestone. The gneisses were in some cases 

 huge intrusions of granite connected with the up-and-down move- 

 ments referred to, and in other cases conglomerates, formed 

 close to the coast-line by waves or rivers. It is probable that 

 there was life of the lower forms in these seas, their skeletons 

 being now altered beyond all recognition. 



Between the deposition of the crystalline schists and the 

 next succeeding strata there is a vast gap, yet the mere existence 

 of a gap in the geological record means something, and we may 

 interpret it as marking a period of uplift in that area, so that it 

 was dry land, and instead of receiving further deposits, became 

 the source of deposits laid down in neighbouring seas. In the 

 vast period of time that this gap represents, most of the altera- 

 tion and folding of these rocks took place, for the later strata 

 are comparatively undisturbed. The mechanics of these huge 

 earth-movements are hidden from us, but they partook of the 

 character of a shrinkage, and the strata were folded and plicated 



