J. D. Dana—Driftless Interior of North America. 251 
cover the whole area (some mountain ridges not being con- 
i the Sierra Nevada ; 
from Iowa and Minnesota to Salt Lake City ; and from Minne- 
sota northward and westward. The line of four inches, as 
the copied portion of the chart shows, passes along the eastern 
ter diverges eastward—continues northward along the summit 
of the mountains. i 
In contrast with this, the winter precipitation over New 
England is 8 to 12 inches; over New York, 6 to 10 inches; 
over Ohio and Indiana, 8 to 10 inches; over the Southern 
States, from Virginia to Georgia and Louisiana, 10 to 20 inches. 
On the chart No. 2 is given the amount of annual precipita- 
tion for this same region. While this amount is 40 to 45 
inches in New England; 40 to 50 inches from Pennsylvania 
southwestward; and 40 to 45.over Ohio and Indiana, the line 
of 20 inches (half the average for New England, Pennsylvania, 
hio, and Jess than half for the more Southern States) crosses 
Western Minnesota and passes just west of Iowa; and the 
line of 16 inches enters Minnesota. Mr. Schott’s chart shows 
less up to 16 inches embraces (exclusive of parts of the 
lines, and especially those of the summer, bend far ire ne 
over the dry region. The climate consequently woul piles 
necessarily occasioned over this central and western eepn ee 
_ continent, only a small amount of precipitation m - th ee : 
~ era; and all the observed glacial facts prove positively tha 
+S a wares portions, the line 2 of No. 1, and 16, 20 and 24 of No. 2, are, 
according to Mr, Schott, only approximati 
