214 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 2 



the succession of the pre-Cambrian rocks or indeed whether great 

 thicknesses of sedimentary rocks, classed by some workers as pre- 

 Cambrian, may not be Cambrian or even later in age. But it is 

 quite clear that in the so-called Algonkian or upper part of the series 

 the thicknesses of sedimentary rocks, associated with contemporane- 

 ous lava flows, reach enormous proportions. 



On the Keweenawan Peninsula of Michigan, the Upper Cambrian 

 sandstones rest upon a great series of conglomerates, coarse red and 

 white sandstones which are often feldspathic, and indicate accumula- 

 tion under arid conditions, somewhat resembling, therefore, the 

 Torridon sandstone of Scotland. Below the Keweenawan series 

 come the Animikie and Huronian series. The Animikie sediments 

 appear to have been formed in an extensive series of fresh-water or 

 saline lakes, into which rivers carried their sediment, and the iron 

 ores of this formation may be analogous to the bog iron ore of 

 present-day lakes and swamps. 



The Huronian contains at least 10,000 feet of clastic deposits and 

 appears to be of continental origin and probably represents river 

 flood-plain and alluvial fan deposits with lake-delta conditions. 

 True bowlder-clay beds are associated with this series. True red 

 arkoses also occur at the base, and these are succeeded by red jasper 

 conglomerates, white quartzite and chert, with limestone and slate. 

 In the so-called Archean, below the Algonkian, are also found tens 

 of thousands of feet of sedimentary rocks such as the Sudburian series. 

 Tliis series has at the base about 5,000 feet of arkose material which 

 appears to have been derived from some distance, as the material 

 is unlike anything in the district. 



The amount of mechanical deformation which some of these 

 originally sedimentary rocks of pre-Cambrian age have undergone 

 in North America make it difficult to assign a source of origin to them 

 with any certainty, but such evidence as there is points to a northerly 

 and northeasterly source. In this connection it is to be noted that 

 some of the formations, like the Animikian, occur in scattered areas 

 of the Canadian Shield and stretch away far into the Arctic regions. 



In Greenland and Spitsbergen nothing corresponding to the Torri- 

 donian or Sparagmite has been found, but in both occur a series of 

 rocks consisting of quartzite, phyllites, limestone, and dolomite, 

 known in Spitsbergen as the Heckla Hook group and certainly older 

 than the Devonian. This series has by some authorities been as- 

 signed to a pre-Cambrian age, and it has in Spitsbergen, like the 

 Archean on which it rests, been profoundly affected by earth move- 

 ments while the Devonian above retain their horizontality, except in 

 the west of Spitsbergen. 



