506 F. H. KXO^'LTOX EVOLUTIOX OF GEOLOGIC CLIMATES 



ETIDEXCE OF THE FLORAS 



Algonkian flora. — So far as now known, the first plants of which we 

 have a definite record occur in tlie Algonkian formations of the Cor- 

 dilleran area of western America. From these beds, which are more 

 than 5,000 feet thick and fnlly 6,000 feet below the overlying Cam- 

 brian, Mr. Walcott ^ has described 6 genera and 10 species of organisms 

 that had the power of secreting and depositing calcium and magnesitmi 

 carbonate. They appear to be algse closely allied to the Cyanophyceae, 

 or bine-green algae, and are believed to have been largely instrumental iu 

 depositing the great pre-Cambrian limestones of western America. Tlie 

 waters in which these algae lived are thought to have been fresh. 



These organisms are so obscure and still so httle understood that it 

 is hazardous to venture an opinion as to the temperature conditions under 

 which thev niisfht have lived. Walcott makes the followino^ observation:; 

 as to the climate of the time : 



••The presence of great thicknesses of red sandstones and shales in the 

 Algonkian sections of the Grand Canyon and Belt series of Montana suggests 

 an arid, possibly a cold, climate. Opjwsed to this are the great limestone beds 

 which indicate a fair supply of water to form inland seas whose temperature 

 was sufficiently high to permit of an adequate growth of algie of a simple type 

 that served as the agency for the precipitation of vast quantities of calcareous 

 matter.'" 



At this point I may stop for a moment to consider the deductions to 

 be drawn from the presence of red beds. Most geologists interpret 

 the presence of red beds as an indication of aridity. On the contrary, 

 it seems to me that the evidence is fairly conclusive that red beds may 

 have been formed under conditions of warm, moist climates. Briefly, 

 the reasons for this view are as follows: 1. So far as known, red beds 

 are not being formed at the present time in any desert region, but as 

 maturely weathered residual soils they are being formed in southern 

 temperate and tropical regions, and in warm, moist climates. 2. Tho 

 plants found in red beds, as, for example, in the Permian, Triassic, 

 etcetera, are not pinched or depauperate, nor do they exhibit marked 

 xorophvtic adaptations. Moreover, very considerable deposits of coal 

 are found in red beds in many parts of the world, which implies the 

 presence of swamps but little above sealevel. 



On the basis of the assumption that the extensive red beds in tho 

 Algonkian indicate warm, moist climatic conditions, and that the algfc 

 call for warm waters. I venture to interpret the climate of at least 



3 C. D. Walootr : Pre-Cambrian Algonkian algal flora. Smithsonian Misc. Coll., vol. 

 64. no. 2. 1014. pp. 77-150. pis. 4-23. 



