lOO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



The fauna of the Greyson shales occurs toward the base of the 

 formation. Collenia iindosa is found at many horizons in the Spo- 

 kane shales, and the Newland limestone algae are reported by Air. 

 M. Collen to occur throughout the section of that formation on the 

 eastern slope of- the Big Belt Mountains. 



THE ALGAL FLORA 



The algal flora of the Algonkian and the Cryptosoon-like species 

 from the Cambrian and later formations are now considered to have 

 been deposited through the agency of algae similar in type and 

 activity to the (Cyanophyceae) Blue-green Algse. No traces have 

 been seen of the fine stems of the algae but single cells and strings 

 of cells have been found with a magnification of 260 diameters. 



In the fresh-water lakes of the present time the Blue-green algae 

 form a thin felt-like layer over some object either minute or large 

 as the case may be. As the under side of this layer dies the outer 

 surface sends the delicate slender stems out into the water until 

 these in turn become twisted and matted together and added to the 

 inner layer. If there is bicarbonate of lime or magnesia in the 

 water a portion is taken up by the algse and deposited in the labora- 

 tory existing in the matted portion of the inner layer and added to 

 the thin layer of calcareous matter. The result is shown in sections 

 of " Lake Balls " illustrated by the figures on plate 4. Some genera 

 and species of the algae build up concentric forms like those shown 

 on plate 4, while others build up sponge-like masses that form solid 

 beds along the shore or in shallow portions of the lake (pi. 4, fig. 4). 



The examination of a large series of the Algonkian and Cambrian 

 algae illustrated in this paper fails to disclose any traces of internal 

 structure (except miroscopic cells) such as occurs in most of the 

 marine algae (Corallinaceae, Characea, etc.), but nearly all have a 

 distinct structure resulting from the deposition of calcium carbonate 

 in certain definite fomis. This may be the simple concentric lami- 

 nation of Collenia (pi. 13), the more complicated Nezvlandia (pi. 6), 

 or the elongate cellular pipe-like Greysonia (pi. 17). 



Comparison of recent Blue- green algcF deposits and those of Al- 

 gonkian time. — On comparing the sections of the " Water Biscuit " 

 (pi. 4) with sections of Collenia (pi. 13) from the Spokane shales 

 of the Belt series of Montana, a striking similarity in their structure 

 is seen. Both are formed of concentric laminations without any 

 apparent structural connection between them as the interspaces are 

 filled in with irregular granulations without any particular method 

 of arrangement. 



