NO. 2 PRE-CAMBRIAN ALGONKIAN ALGAL FLORA IO3 



fresh water deposits with N ewlandia, Camasia, Collenia and Crypto- 

 zoon, that water plants similar to the Blue-green algse were the 

 agents that built up the fossil algal flora of the Algonkian, I asked 

 my friend Dr. Albert Mann, the microscopist, if he would not study 

 thin sections of the rock in which the specimens occur, also the resi- 

 dual mud resulting from the dissolving of the algal limestone by 

 hydrochloric acid. He very kindly consented, and soon found in 

 the residual material many single cells and groups of cells such as 

 occur in the recent Chroococcacese (pi. 20, fig. 5) and rows of cells 

 similar to those of the recent Nostocacese. 



A row or chain of cells derived from Camasia spongiosa is shown 

 by figures 2-4, plate 20. Figure 4 is from an untouched photograph 

 (x 350). Owing to the chain or filament not being in the same 

 plane from end to end many of the cells are not in focus in figure 

 4. In order to correct this the entire series of cells have been out- 

 lined in figure 2, and in figure 3 this is further enlarged so as to 

 show the outline of the cells. The same conditions exist in a chain 

 of cells in a filament of a recent Blue-green alga, Schizothrix, from 

 the surface of a calcareous deposit in Green Lake, New York. 

 Figure 8 is from an untouched photograph, and figure 8a shows 

 the full length of the chain. The chain represented by figures 2-4 

 is embedded in a very thin plate of opal-like silica. 



Figure 5 represents a cluster of round cells (x 350) with their 

 outline strengthened, and figure 5a as they appear in the untouched 

 photograph. A group of longitudinally arranged cells is shown by 

 figure 6a, and in the untouched photograph represented by figure 6. 

 A group or chain of cells of a recent, calcareous depositing Blue- 

 green alga is shown by figure 7 (x 1,200). This may be compared 

 with figure 3 from Camasia spongiosa of the Newland limestone. 



A number of very thin opal-like siliceous plates show minute 

 tubes such as are illustrated by figure i. These appear to be of 

 organic origin and may represent minute tubes similar to those 

 found in some genera of Blue-green algse. 



Bacteria. — Although the existence of Bacteria in Algonkian time 

 has not been demonstrated from the observations already given (pp. 

 92-94) ; it is quite probable that the Bacteria were a most important 

 factor in the deposition of the Algonkian limestones. 



Classiiication. — For the purpose of grouping the various forms of 

 the algal flora of the Algonkian the following classification is made 

 from external fomi. 



