420 THE JOURNAL OF GEOLOGY. 



(d) The Tennessee type, prevailing in Kentucky, Tennessee, Arkansas, Missis- 

 sippi and Alabama, has the highest rainfall the last of winter, while the mini- 

 mum is in mid-autumn, (e) The Atlantic type, covering all the coast save 

 New England, is one where the distribution throughout the year is nearly uni- 

 form, with a maximum precipitation after the summer solstice, and a mini- 

 mum during mid-autumn, (f) The St. Lawrence type is characterized by 

 scarcity during the spring months, heavy rainfall during the late summer and 

 late autumn months, with a maximum during November. 



The regions lying between these several type-regions have composite rain- 

 fall types, resulting from the influence of two or more simple types. 



H. B. K. 



The Geographic Development of the Eastern Part of the Mississippi 

 Drainage System. By Lewis G. Westgate, Middletown, Conn. 

 (American Geologist, Vol. XI, April, 1893, 15 pp.) 



The drainage of the Eastern Mississippi basin in post-carboniferous was 

 in all probability consequent upon the tilting which accompanied the stronger 

 folds of the Appalachian revolution in the east. The present drainage is 

 found to accord in the main with this hypothetical post-carboniferous drain- 

 age, but several streams depart quite widely from it. 



(a) The great drainage lines of the St. Lawrence basin are structural 

 valleys developed along the strike of the softer Paleozoic strata, and at right 

 angles to the original surface. The streams seem, therefore, to have adjusted 

 themselves to the differences in hardness and structure of the beds discov- 

 ered, (b) The Ohio and Cumberland rivers cut directly across the Ten- 

 nessee and Cincinnati anticlines. The most probable explanation is that the 

 rivers were superimposed upon the arched and eroded Silurian rocks from a 

 thin cover of carboniferous beds — now entirely removed, (c) The Upper 

 Mississippi does not follow the dip of the rocks to the southwest, but follows 

 the strike to the southeast. This part of the river probably dates from the 

 elevation of the plains on the west and the Appalachians on the east, which 

 marked the close of the Cretaceous and which left a broad north and south 

 valley, (d) The author finds good reason to believe that the Lower Missis- 

 sippi, in post-carboniferous times, flowed west through Missouri and Arkansas. 

 The present course was probably taken at the close of the Cretaceous in con- 

 sequence of elevations on the west and east, and possible depression in the 

 south. 



The Cretaceous base-level recognized by Davis on the Atlantic slope can 

 be traced more or less discontinuously, and remnants of it are believed to 

 exist in Kentucky, Tennessee, Wisconsin, Minnesota and Arkansas. But in 

 general the work of the Tertiary cycle has obliterated almost all evidence of 

 it on all but the hard sandstones and conglomerates of the Paleozoic series. 



