80 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



Dr. George T. Moore, Director of the Missouri Botanical Garden, 

 referred me to authors who had written on the deposition of Hme 

 and magnesia through the agency of algas, and Dr. M. A. Howe of 

 the New York Botanical Garden sent a number of publications 

 bearing on the coralline algae. 



I also consulted with Dr. T. Wayland Vaughan, of the United 

 States Geological Survey, and Dr. Austin H. Clark, of the United 

 States National Museum, in regard to the recent calcareous algae. 



CONTINENTAL CONDITIONS DURING ALGONKIAN 

 TIME 



The character and structure of the pre-Algonkian formations ' 

 indicate that toward the close of the Archeozoic era a period of 

 world-wide diastrophism ensued, resulting in the receding of ocean 

 waters or in the uplift of the American and all other continental 

 masses in relation to the oceans. This great change (Laurentic 

 Revolution) was accompanied or followed by local disturbances 

 which produced profound folding and the metamorphism of the pre- 

 Protero'zoic complex, with the formation of mountain ranges, up- 

 lands, valleys and lowlands. 



Two broad continental geosynclines subparallel to the western 

 and eastern coast lines of the North American continent began to 

 form early in Algonkian (Proterozoic) time. When cut off from 

 the outer oceans or while the surface of these great areas was above 

 the level of marine waters, they received terrigenous Algonkian 

 sediments which began to accumulate on river flood plains and other 

 favorable areas, or were deposited in the epicontinental fresh and 

 brackish water seas or lakes that filled the shallow depressions 

 within the area of the geosynclines. The western or Cordilleran 

 geosyncline extended from the vicinity of the head of the Gulf of 

 California northward probably to the Arctic Ocean. 



In Arizona what is left of the Algonkian period of sedimentation 

 is represented by nearly 12,000 feet (3,658 m.) in thickness of 

 sandstones, shales, and limestones of the Grand Canyon group. In 

 Utah and Nevada sediments forming only sandstone and siliceous 

 shale appear to have gathered, while in Montana there is a develop- 



^Van Hise and Leith, Monogr. U. S. Geol. Survey, Vol. 52, 191 1. Table 

 facing p. 598. Also see map i, accompanying Bull. No. 360, U. S. Geol. Sur- 

 vey, 1909. 



