112 THE CANADIAN NATURALISiT. ToL 



VI. 



GEOLOGY AND MINERALOGY. 



Prop. Newberry on the Ancient Lakes of AYestern 

 America. — The following extracts from an article by Dr. New- 

 beiry, contributed to the American Naturalist, and intended to 

 form a part of Dr. Hayden's forthcoming work, — Sun Pictures 

 of the Pvocky Mountains — will be read with interest, 

 extract relates to the topography of the region referred to : — 



Without going into details or citing the facts or authorities on 

 which our conclusions rest, I will, in a few words, irive the cene- 

 ralitiesof the geological and topographical structure of that portion 

 of our continent which includes the peculiar features that are to be 

 more specially the subject of this paper. 



It is known to most persons that the general character of the 

 topography of the region west of the Mississippi has been given 

 by three great lines of elevation which traverse our territory from 

 north to south; the Rocky Mountain Belt, the Sierra Nevada and 

 the Coast Ranges. Of these, the last is the most modern, and is 

 composed, in great part, of Miocene Tertiary rocks. It forms a 

 raised margin along the western edge of the continent, and has 

 produced that " iron bound coast" described by all those who have 

 navigated that portion of the Pacific which washes our shores. 



Parallel with the Coast Mountains lies a narrow trough which, 

 in California, is traversed by the Sacramento and San Joachin 

 Rivers, and portions of it have received their names. Further 

 north, this trough is partially filled, and for some distance, nearly 

 obliterated by the encroachment of the neighboring mountain 

 ranges, but in Oregon and Washington it reappears essentially the 

 same in structure as further south, and is here traversed bv the 

 Williamette and Cowlitz Rivers. 



These two sections of this great valley have now free drainage 

 to the Pacific, throuah the Golden Gate and the trou2;h of the 

 Columbia, both of which are channels cut by the drainage water 

 through mountain barriers that formerly obstructed its flow, and 

 produced an accumulation behind them that made these valleys 

 inland lakes ; the first of the series I am to describe of extensive 

 fresh-water basins that formerly gave character to the surface of 

 our Western Territory, and that have now almost all been drained 

 away and have disappeared. 



