242 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1915. 



tor in the deposition of the Algonkian limestones, but no definite 

 bacteria had been discovered. From specimens collected in the sum- 

 mer of that year many thin sections were prepared, and in these Dr. 

 Albert Mann, microscopist and student of diatoms and bacteria, dis- 

 covered individual cells and apparent chains of cells (pi. 4, figs. 2 

 and 3) which correspond in their physical appearance with the cells 

 of micrococci (pi. 4, fig. 1), a form of bacteria of to-day. The world 

 at large has believed that bacteria were modern forms of life, but 

 they had been found as explained aboA'e in fossil wood of Carbonifer- 

 ous time and now we are made to realize that they existed in the first 

 known epoch of the earth's life history, many millions of years ago. 



For the purpose of comparison an illustration is given of a group 

 of recent forms as illustrated in the Encyclopedia Britannica^ and 

 of the form of cells shown in the thin sections cut from the fossil 

 algal remains of the Newland limestone (pi. 4). 



ALGONKIAN FOSSIL ALGAL REMAINS. 



In Montana it was found that a great series of pre-Paleozoic sedi- 

 mentary rocks was exposed by the uplift of the granite mass form- 

 ing the summit of Mount Edith of the Big Belt Mountains, in such 

 a way that the thickness of the sandstones, limestones, and shales 

 could be readily measured in the numerous sections exposed in the 

 canyons worn by waters descending from the higher points to the 

 valley surrounding the range. Nearly 5 miles in thickness of rock 

 were measured, and in them limestone reefs of fossil algal remains 

 were found and large numbers of typical specimens were collected. 



It was observed that some of the algal remains were deposited 

 very much in the same manner as those that are now being deposited 

 in many fresh-water lakes, and that many of the forms had a charac- 

 ter similar to those being deposited through mechanical and algal 

 agencies in the thermal springs and pools of the Yellowstone Na- 

 tional Park. A comparison of microscopic cells from recent blue- 

 green alga3 and their Algonkian representatives disclosed surprising 

 similarity (pi. 5) and led to the conclusion that this type of alga 

 existed very early in the history of life. 



On the north side of the East Gallatin River two very rich beds 

 of algal remains were found, many of which, on account of the fos- 

 sil being silicified and imbedded in a softer limestone, were weathered 

 out in relief, as shown by plate 3. 



1 Eleventh ed., vol. 3, p. 160, fig. 5. 



