ALGONKIAN LIFE 363 



The lower part of this series is formed by thick lava sheets, inter- 

 bedded with sandstone and conglomerate, and above is a mass of 

 sedimentary rocks largely derived from the volcanic materials. 



Over the great Archsean area of Canada occur many districts 

 of metamorphic rocks which are plainly of sedimentary origin, 

 such as crystalline limestones, schistose conglomerates, as well 

 as volcanic tuffs and agglomerates. In this region and in New 

 England the Algonkian metamorphics apparently grade into the 

 Archsean complex without unconformity. This apparent conformity 

 may. however, very well be due to subsequent dynamic metamor- 

 phism, which, as has been proved, may obliterate nearly all traces 

 of a great unconformity. Through the Rocky Mountain region and 

 the Pacific coast mountains, the Archaean is in very many places 

 overlaid by great thicknesses of metamorphic Algonkian rocks, 

 such as quartzites, sandstones, and schists, which are sometimes as 

 much as 12,000 feet thick, as in the Wasatch and Uinta mountains. 

 Other isolated areas are found, as in the Black Hills, where a great 

 mass of schists, slates, and quartzites is separated by a very marked 

 unconformity from the overlying Cambrian ; also in Missouri and 

 Texas. The Algonkian rocks of the West have not been subjected 

 to such extreme folding as have those of the East, and hence 

 their distinctness from the Archaean is more clearly marked. 



In other continents the distinction has hardly been drawn yet 

 between the Archaean and the Algonkian. In Great Britain, how- 

 ever, are found very interesting parallels with the Algonkian of this 

 country. In Scotland the Torridon sandstones, 8000 to 10,000 

 feet thick, which are nearly horizontal and almost unchanged, 

 lie unconformably between the oldest Cambrian and the basal 

 Archaean ; and in other areas, metamorphic rocks of sediment- 

 ary origin occupy a similar position. Many of the crystalline 

 schists of the European pre- Cambrian areas appear to correspond 

 in character and position to the metamorphic Algonkian. 



Life in the Algonkian. — In the Grand Canon and the Lake 

 Superior region determinable fossils have been found in the less 

 changed sediments, but they are too few and scanty to tell us 

 much of the life of the times. It must also be remembered that 



