umpleby: stratigraphy of idaho 49 



GEOLOGY. — Note on the stratigraphy of east-central Idaho. 

 J. B. Umpleby, Geological Survey. 



During recent field studies much additional information has 

 been obtained concerning the stratigraphy of east-central Idaho. 

 During September 1910 the writer examined the area about the 

 head of Lemhi Valley, and a year later, in company with Dr. 

 George H. Girty, revisited the locality about Gilmore and made 

 a fairly complete collection of fossils. 



The Paleozoic section at Gilmore is made up of a great succes- 

 sion of sedimentary rocks, striking north-south and usually dip- 

 ping about 45° east. Cambrian, Ordovician, Silurian, Devonian 

 (?) and Mississippian formations are present. At the base is a 

 clear-white, fine-grained quartzite at least 2,000 feet thick. It 

 is well exposed above Meadow Lake. Conformably above it is 

 massive blue dolomitic limestone about 500 feet thick. This is 

 assigned to the Richmond stage of the Ordovician. Then fol- 

 lows 300 feet of massive white dolomitic limestone of Silurian 

 age. The formation next above comprises about 2,000 feet of 

 thin-bedded blue and white dolomitic limestones, with occasion- 

 ally a siliceous band. This formation is tentatively considered 

 as Devonian. It is presumably conformable with the Mississip- 

 pian, altho its upper contact was not seen. Only a portion of the 

 latter formation is exposed, but from this it is known to be more 

 than 300 feet thick. 



The Paleozoic series rests upon intensely metamorphosed rocks 

 of Algonkian age which outcrop along its western border. On the 

 east it disappears beneath Miocene lake beds. Mesozoic forma- 

 tions are absent. 



EVOLUTION. — Evolution in discontinuous systems. II 1 . Alfred 

 J. Lotka. Communicated by J. A. Fleming. 



One of the principal types of change of state with which we are 

 concerned in discussing inter-group evolution in biological sys- 

 tems is the passage of matter from one kindred-group into another 

 thru the process of " feeding," the one group serving as food for 



x See this Journal 2: 2. 1912. 



