

(7\c 



CHAPTER V 

 THE PROTEROZOIC ERA 



The Proterozoic era, represented by the Algonkian system of 

 rocks, includes the time between the Archeozoic and the earliest 

 Paleozoic (Cambrian) period, the Cambrian system comprising 

 the oldest known rock system with abundant fossils. 



Great Unconformity between the Archean and Algonkian 

 Systems. — As already stated, wherever observations have 

 been made under favorable conditions, the summit of the Archean 

 complex appears to be marked by a profound unconformity. Such 

 an unconformity, however, cannot be universal because the very 

 fact of extensive erosion of certain areas implies the deposition of 

 the eroded sediments in other areas. Such sediments, if found, 

 would contain the records of the time interval indicated by the 

 great unconformity. So far at least, this sedimentary record has 

 not been brought to light, probably either because (1) these sedi- 

 ments were deposited in ocean basins not since exposed as dry 

 land; or (2) these sediments are not at present exposed to view 

 because concealed under later formations; or (3) these sediments 

 have not been recognized as such. Also it is not at all unlikely 

 that some or even many of these sedimentary areas may subse- 

 quently have become land areas so that, as a result of erosion, more 

 or less of the sediments were again removed to again be deposited 

 as Proterozoic or later sediments. Future researches may bring 

 to light some of the now "lost records" which represent the great 

 unconformity or time gap between the Archeozoic and Proterozoic. 



General Character and Origin of the Algonkian Rocks. — 

 Emphasis should be placed upon the fact that the Proterozoic was 

 the first era during which ordinary processes of weathering, erosion, 

 and deposition of great series of strata became dominant processes, 

 such processes having been dominant ever since. Judging by the 

 records, the Proterozoic, on one hand, was marked by less igneous 

 activity than the Archeozoic, while, on the other hand, it was 

 marked by distinctly more igneous activity than any subsequent 



47 



