340 W. H. Tivenhofel — Pre-Cambrian and 



have taken in tke building of some divisions of the Pre- 

 Canibrian limestones. The data have been chiefly 

 derived from the Rocky Mountain region, but that is 

 probably due to the fact that paleontologic studies of 

 Pre-Cambrian rocks have been to a very great extent con- 

 fined to that region. There is little doubt that algal 

 deposits will ultimately be found to be equally abundant 

 in all other Pre-Cambrian terranes during the formation 

 of which conditions obtained which were adapted to the 

 presence of algae. Doctor C. K. Leith's photographs of 

 some of the rocks to the east of Hudson Bay 3 show that 

 algal deposits are abundant in some of the limestones of 

 that region and in the paper by Doctor Grout and in this 

 paper it will be shown that they are also extremely abun- 

 dant in some Pre-Cambrian terranes of the Lake 

 Superior country. 



The contributions of the algae to modern deposits are 

 of great importance and in the building of the "coral 

 reefs" they appear to have played a role that from a 

 quantitative point of view is equal to that of any other 

 organism. At Funafuti the relative importance of the 

 organisms forming the reef were Litliotliamnium, Hali- 

 meda, Foraminifera, and lastly the corals, 4 while about' 

 the Murray Island coral reef (north end of the Great 

 Barrier reef) at 200 feet from the shore the algae consti- 

 tute 42-5% of the sediments and the corals 34-6%. At 

 1600 feet from the shore the algae make 32-6% of the sedi- 

 ments and the corals 41-9 %. 5 



In the Carboniferous rocks of Great Britain, Professor 

 E. J. Garwood has found algal deposits in abundance in 

 some horizons and he personally suggested to the writer 

 that such would likely be found to be true for American 

 Carboniferous strata. 6 In the highest Ordovician forma- 

 tion (Stage 5) of the Kristiania region of Norway, entire 

 beds of limestone are composed of algal remains and in 

 Gotland the 8 pongio stroma and Sphaerocodium marls 

 and limestones receive their names from the abundance 

 of algal material. 7 



8 Recently described by Moore, J. C. : Jour. Geol., vol. 26, pp. 412-413, 

 1918. 



4 Howe, M. A.: The Building of " Coral Reefs"; Science, vol. 35, pp. 

 837-842, 1912. 



5 Vaughan, T. W., and Goldman, M. I.: Papers from the Dept. Marine 

 Biology of the Carnegie Institution of Washington, vol. 9, pp. 255-258, 1918. 



6 Garwood, E. J. : Geol. Mag., Dec. VI, vol. 1, pp. 265-271, 1914. 



7 Munthe, H. : Guide Book, No. 19, Xlth Internation. Geol. Cong., 1910. 



