SEP 20 1900 



DESCRIPTION OF LAKE BED5. 



Since cominj? to Moutaua in the spring of 1894, I tiave spent mucli 

 of my time in studying the lalte bed deposits in tlie western part of 

 tlie state, and in collecting and studying the vertebrate fossils found 

 in them. 



These deposits occur in nearly every large valley in the moun- 

 tain regions. I have myself observed them in the valleys of the 

 upper Missouri (above the region of Helena), Gallatin, Madison, Jeffer- 

 son, Beaverhead, Ruby (Stiukingwater), Big Hole, Hell Gate, and 

 Bitter Root rivers, and their tributaries. 



Hayden and Peale, in the Annual Reports of the U. S. Geol. Sur. 

 of the Territories for 1871 and 1872, have given very good general de- 

 scriptions of these beds. 



These fresh water lakes filled the valleys and at some time, east of 

 the main divide, left only the tops of the mountains standing as islets, 

 long islands, and peninsulas in the waste of waters. West of the 

 divide the land masses were larger. 



Though over a good share of the area of the ancient lakes there 

 are no good exposures yet it is not a difficult matter to ascertain ap~ 

 proximately their former extent by the topography of the country and 

 the occasional outcrops. The sands and clays that compose the de- 

 posits are often grassed over, covered with drift, or entirely washed 

 away; yet in some of the valleys there are good and quite extensive 

 exposures. One strip fifteen to twenty miles long near the Madison 

 forms a miniature "Bad Land." 



At one time there was a large irregular shaped lake extending 

 from about ten to twenty miles north of Helena, southeastward, and 

 then southward about seventy miles, to the vicinity of Pony, m 

 Madison county, on a line nearly west of Bozeman; and, probably, over 

 the rather low and narrow divide to the south and up the Madison 

 valley about sixty miles farther, making the whole distance between 

 one hundred and thirty and one hundred and forty miles. Its greatest 

 width from the vicinity of Bozeman to that of Whitehall was at least 

 sixty miles. To the south westward an arm extended up the Beaver 

 Head and its tributaries nearly or quite to the main watershed of the 

 Kooky jMountains south of Dillon. It extended eastward to Vir- 

 ginia City, and probably across the divide to the east connecting 

 with the waters of the Madison valley, so the South Boulder moun- 

 tain range was an island or peninsulk. The Ruby Mountains were 



