NO. 2 PRE-CAMBRIAN ALGONKIAN ALGAL FLORA 9I 



definite physiographical conditions similar to those which obtain to-day in the 

 neighborhood of coral reefs. Such lagoon conditions would tend to come into 

 existence during periods of subsidence or elevation, and this is just what we 

 find when we examine the periods at which these reefs are most persistent. 



Thus the Girvan Ordovician lagoon-phase occurred during an elevation 

 which culminated with the deposition of the Benan Conglomerate; the Lower 

 Carboniferous "Algal band" in Westmorland was laid down during the 

 subsidence which followed the Old Red Sandstone continental period, while 

 the Upper Girvanella Nodular band occurred when the marine period of the 

 Lower Carboniferous was drawing to a close and a general elevation was 

 taking place. Similar conditions could be drawn from the Gotlandian and 

 other periods recorded above. 



A table which shows the known occurrence of fossil algse from 

 the Cambrian to the late Tertiary accompanies the paper. 



A brief paper by Dr. Marshall A. Howe of the New York Botani- 

 cal Garden on " The Building- of Coral Reefs," ^ cites a number of 

 writers to sustain his contention that the calcareous algse are the 

 largest contributors to the building of the " Coral Reefs and 

 Islands." Dr. Howe in summing up on his subject says : 



With the dominance in reef-building activities resting sometimes with the 

 calcareous algse and sometimes with the corals, and with the Foraminifera 

 and other groups also playing their parts, the problem of determining the 

 " most important " constructive element in the calcium carbonate reefs of 

 the world, ancient and modern, is naturally a most complicated and difficult 

 one, and one that may never be solved to the full satisfaction of those most 

 interested.^ 



As an illustration of the dominance of the lime secreting plants he 

 quotes Prof. J. Stanley Gardiner as follows : 



The reefs of the Chagos are in no way peculiar, save in their extraordinary 



paucity of animal life However, this barrenness is amply compensated 



for by the enormous quantity of nullipores iLithothaninia, etc.) incrusting, 

 massive, mammillated, columnar and branching. The outgrowing seaward 

 edges of the reefs are practically formed by their growths and it is not 

 too much to say that were it not for the abundance and large masses of these 

 organisms, there would be no atolls with surface reefs in the Chagos.* 



Again he quotes Professor Seward's summary of the results of 

 J. Walther's studies of a Lithothamnion bank in the Bay of Naples 

 about 30 m. below the surface of the water : 



By action of the percolating water the Lithothamnion structure is gradually 

 obliterated, and the calcareous mass becomes a structureless limestone. 



' Science, n. s.. Vol. 35, 1912, pp. 837-842. 



" Idem, p. 842. 



^ Trans. Linn. Soc. London, Zool., 2d ser.. Vol. 12, pp. 177, 178, 1907. Also, 

 Nature, Vol. 72, pp. 571, 572, where a photograph of this Lithothamnion reef 

 is published. 



