NO. 2 TRE-CAMBRIAN ALGONKIAN ALGAL FLORA II7 



Observations. — Recently when reading- an account by Dr. A. C. 

 Peak of the pre-Cambrian rocks of the region between the Missouri 

 River and Dry Creek, a tributary of the East Gallatin River, Gallatin 

 County, Montana. I noted that he described the occurrence of 

 numerous flattened concretions in an Algonkian limestone ' which 

 the people in the vicinity called fossil turtles. On incjuiring- 

 of Dr. Peale he told me that there was a specimen in the United 

 States National ]\luseum. Upon examining it there was very little 

 to indicate that it was more than an ordinary septaria-like concre- 

 tion. Cutting a cross section on one side and treating it with acid 

 the wonderful interior and exterior structure was developed that 

 is shown in the accompanying illustrations. Dr. Peale states that 

 the "concretions" measure several feet in diameter and from 6 to 

 12 inches (15.4 to 31 cm.) in thickness, and that they occur in a 

 limestone. 



An examination of the residual sediment resulting from dissolving 

 some of the limestone matrix shows microscopic cells much like 

 those found with Cryptocoo)i and Collcnia. 



I anticipate visiting the locality where Dr. Peale collected the 

 specimen described and hope to be able to give a much fuller account 

 of the occurrence and character of this remarkable addition to the 

 Algonkian algal flora. 



Formation and locality. — Algonkian: (400J) Belt terrane ; north 

 side of Gallatin and East Gallatin Rivers, north of Bartons Bridge, 

 west of Hillsdale Postoffice, Gallatin Countv, ^lontana (A. C. Peale, 

 1885). 



After this paper was in page proof I received from Dr. G. R. 

 Wieland a copy of his paper on " Further Notes on Ozarkian Sea- 

 weeds and Oolites " ' in which he discusses the various forms 

 that have been referred to Cryptocoon. This important contribution 

 to the subject of fossil algae will be referred to in any future study 

 I may make of the pre-Cambrian fossil algse. 



Bull. U. S. Geol. Survey. No. iio. 1893, p. 17. 



Bull. American Museum Nat. Hist., Vol. 33, pp. 23/-260. 



