NO. 2 PRE-CAMBRIAN ALGONKIAN ALGAL FLORA lOI 



The mode of growth of the recent and ancient forms has many 

 points in common. The " Water Biscuit " are found on the muddy 

 or sandy lake-bottom ; in some places quite abundant and in others 

 more scattered. The specimens of Collenia from the Spokane shales 

 occur embedded in a very fine arenaceous shale, sometimes in great 

 numbers. That they were fonned on the muddy bottom of a body 

 of water which was shallow, is shown by the presence of ripple 

 marks and sun cracks at various horizons in the shales. The speci- 

 mens of Collenia vary in size from the size of a mustard seed up to 

 a foot or more in diameter, and usually occur with the flattened or 

 hollow side downward. They may be scattered about singly or in 

 groups or attached to each other so as to form a mass of calcareous 

 nodules. 



There is considerable siliceous matter occurring in the laminations 

 of Collenia and also dolomitic partings between the laminations of 

 growth although all openings in the original specimen are now filled 

 with a dark bluish-gray limestone. 



Another case of resemblance between a deposit made by Blue- 

 green algse and the Algonkian fossil algae is seen by comparing a 

 section of a fragment of a large deposit in a fresh-water lake in 

 Michigan (pi. 4, fig. 4) with a section from the Belt terrane that 

 I have named Camasia spongiosa (pi. 12). 



From the fact that the recent laminated lake balls and layer de- 

 posits were largely deposited through the agency of Blue-green 

 algae, it is probable that the same simple types of algae were the 

 active agents in depositing the forms described in this paper under 

 the generic names of Collenia, Neiulandia, Camasia, Kinneyia, 

 IVeedia, Greysonia, and Copperia. The finding of single cells and 

 chains of cells with Camasia spongiosa is a most important factor in 

 establishing the presence of the (Cyanophyceae) Blue-green algae- 

 like forms in connection with the Algonkian forms listed above. 



Mode of growth. — In the absence of sticks of wood, stones and 

 other solid objects upon which to start their growth, as do the 

 modern Blue-green algae, the Algonkian forms evidently started and 

 built up their structures on bits of hardened mud and often on 

 fragments of algal deposit broken up by current or wave action. 

 Most of the forms spread out along the surface of the muddy bot- 

 tom until they were buried beneath an influx of ooze or mud that 

 filled all the cavities and channels in the algal deposits. In the 

 Newland limestone specimens the filler was a fine calcareous mud, 

 and in those from the Spokane shale an argillaceous mud. One of 



