THE OLDEST ROCKS 
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account, it consists for the most part of a high level 
plateau terminated along the coast by steep escarpments, 
more or less indented by the action of huge overflow 
glaciers. It includes several groups of volcanic islands, 
the chief of which is the Ross Archipelago (Lat. 77''-79°). 
But in this narrative we shall include the Ross Sea and 
the Great Ice Barrier in the region, as inseparably bound 
up with Victoria Land in its history. 
The oldest rocks met with in South Victoria Land, 
forming its foundation, or ' shield,' consist of gneisses, 
schists, quartzites, and crystalline limestones, much 
altered and folded by later earth-movements. On account 
of this alteration, much of their story is hidden from us, 
but we may compare them in age with the 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 lime- 
stones 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 cannot have been less than 15,000 
to 20,000 feet. But figures are of little value, since there 
