THE CENTRAL BASIN OF TENNESSEE. 95- 



and transpoi'ting, whereas an unevenly distributed supply, or where 

 the amount is concentrated into a short period of time at the expense 

 of the rest of the year, erosion is retarded. In the dry season weath- 

 ering is greatly retarded for the lack of assistance from the transport- 

 ing agent ; and in the wet season, although transportation and corra- 

 sion are accelerated, weathering is retarded. Weathering is greatly 

 facilitated by abundance of moisture, but it requires to be evenly dis- 

 tributed. If the rainfall be uniformly distributed a greater amount 

 is absorbed by the soil, and by the perecolating of the water the rocks 

 underneath are dissolved, or at least partially broken up into a 

 condition fit to be removed as soon as the present oveziying soil is 

 taken off. In the case of a concentrated dash of rain coming all to- 

 gether more falls than can be absorbed and it consequently passes off to 

 swell the power of the transporting agent without having done any- 

 thing to aid in providing material to be transported. 



The rainfall within the Central Basin — that is, taking the averages 

 as observed at Nashville as being representative — for the yeai's from 

 1871 to 1887, shews a remarkably uniform rate of precipitation. The 

 average annual precipitation amounts to 51.88 inches distributed 

 over the seasons as follows : — 



Spring 14-09 inches. 



Summer 13-47 " 



Autumn 10-29 " 



Winter 14-03 " 



The average monthly precipitation for a period extending over the 

 same length of time is 4.32 inches, August, September and October 

 being the lowest with averages of 3-41 inches, 3-60 inches and 2-79 

 inches respectively. 



Table III. shews the averages of the monthly and daily precipita- 

 tion from 1871 to 1887. 



Table IV. gives us a record of the excessive and heavy rainfalls at 

 Nashville for seventeen years (1871 — 1887). 



