NO. 2 PRE-CAMBRIAN ALGONKIAN ALGAL FLORA 95 



animal debris. The supposed Micrococci present little that is characteristic; 

 the more definite, rod-like form of the Bacilli ofifers a better means of recog- 

 nition, though far from an infallible one; in a few cases dark granules, sug- 

 gestive of endospores, have been found within the rods. On the whole, the 

 occurrence of Bacteria in Palaeozoic times — so probable a priori — may be 

 taken as established, though the attempt to discriminate species among them 

 is probably futile. 



It may be that traces of bacteria will be found in the Algonkian 

 limestones when the investigations now planned are carried to 

 completion. 



The carbonaceous matter in the dark Newland limestones is shown 

 by the black, floculent residue that accumulates when a fragment 

 of limestone is dissolved in hydrochloric acid, and in the field by the 

 bituminous odor given ofif when the rock is struck with a heavy 

 hammer. The carbonaceous matter of the Bacteria and Algge was 

 probably the source of that occurring in the limestone. 



MAGNESIAX LIMESTONES 



The presence of thick deposits of magnesian limestone in the 

 Algonkian, leads to the conclusion that the magnesium content of 

 Algonkian river and epicontinental bodies of water was not far from 

 what it is to-day. Dr. Stuart Weller asks the question, " Are the 

 Fossils of the Dolomites indicative of Shallow, highly Saline and 

 Wann Seas?"^ He compared the faunas of the dolomitic Galena 

 formation of the upper Mississippi region with that of the Trenton 

 limestone of the eastern or Atlantic region. He concludes that from 

 these comparisons there is 



no evidence whatever for concluding that the life conditions in the Galena sea 

 were in any respect different from those of the basins which are now repre- 

 sented by purely calcareous sediments. There is no single characteristic of the 

 fauna which would suggest that the waters were more saline, warmer, or 

 shallower that the seas in which, for instance, the Trenton limestone of 

 the East or the Kimmswick limestone of southern Illinois and Missouri were 

 deposited. It is ordinarily conceded that an intensification of the salinity 

 of sea waters produces a depauperation of the faunas, but the fauna of the 

 Galena is notably composed of the larger and more robust forms, probably 

 because the smaller and more delicate shells have been obliterated by sec- 

 ondary chemical changes in the sediments.^ 



His summary is that,' 



in conclusion, it may be stated from the evidence of the fossils alone 

 there seems to be no reason for assuming that our widespread dolomitic 



^ Bull. Geol. Soc. America, Vol. 22, 191 1, p. 227. 

 ^ Idem, pp. 229-230. 

 ' Idem, p. 231. 



