266 ANNUAL REPORT SMITHSONIA^i INSTITUTION,*1916. 



It is possible that there were two early ice ages, with an interval 

 between; but it seems more probable that they are of the same age 

 and all really pre-Cambrian. The Australians believe that their 

 more ancient tillites are Cambrian, however. 



Tillites have been suggested at two places in the Keweenawan of 

 America. They occur in the Gaisa beds of Norway, where there is a 

 striated surface beneath; perhaps also in the Torridonian of Scot- 

 land. In Australia Howchin describes an area of 460 miles by 250, 

 and they are found also in Tasmania. They are reported from the 

 Nant'ou formation in China ; the Griquatown series in Cape Colony, 

 where they have an area of at least 1,000 square miles, and near 

 Simla, in India. The last two mentioned may be older than the 

 Keweenawan. Sir Thomas Holland thinks the Simla tillite may even 

 be as old as the Huronian. 



These tillites belong to higher latitudes than those of the Permo- 

 carboniferous, none coming nearer the Equator than 29° ; but some 

 of them occupy regions now warm temperate, while the ice sheets of 

 the Pleistocene halted at about 38° in North and South America and 

 62° in Europe. In so old a period one can hardly expect to find very 

 complete evidence of the area covered by glaciers; but this ice age 

 seems to have been more severe than that of the Pleistocene. 



HURONIAN ICE AGE. 



Much farther off in the abj^ss of pre-Cambrian time is the Lower 

 Huronian Glacial period, thus far known with certainty only from 

 the Canadian Shield, unless the tillite reported by Hintze from the 

 Wasatch Momitains and that from Simla in India are to be referred 

 to so early an age. A characteristic tillite with well-striated stones 

 has been found in the famous Cobalt region, its hard bowlder-clay 

 cut by the richest veins of native silver in the world. Striated stones 

 have been found also 60 miles to the east, in the Province of Quebec, 

 by members of Morley Wilson's geological survey party,^ and one 

 from the original Huronian region, 160 miles to the southwest, has 

 been figured by Collins.^ Areas of similar coarse bowlder conglom- 

 erate or tillite, sometimes inclosing blocks tons in weight and miles 

 from their source, have been mapped at various points as far north- 

 east as Chibougamau, 320 miles from Cobalt, and have been found 

 also to the west of Cobalt. They are widely scattered over the Cana- 

 dian Shield and were once much more extensive, covering, no doubt, 

 many thousands of square miles. 



In most cases the tillite rests Avith gentle dips on the low hills and 

 shallow valleys of a peneplain closely resembling the present Lauren- 



^G. S. C, Mem. 39, pp. 88-97. 



2 G. S. C, Museum Bull., No. 8, plate U 



