174? Mr.Henwood'sZfac/sfofl/77/g on theTheory of the Formation 



I believe I correctly follow Mr. Daniell* in estimating the 

 evaporation " from water, vegetation, or ploughed land " as 

 ecjual; although this does not coincide with Mr. Dalton's ob- 

 servations on the same subject f. 



It has been already remarked, that the computed quantity 

 exceeds that actually delivered ; and if we consider the differ- 

 ence to be one-seventh of the whole, there will still be an ex- 

 cess of 104,407,394?-15 cubic feet J ; nor will our conclusions be 

 much falsified, by omitting the quantity afforded by wells, 

 which probably does not much exceed 10,000 cubic feet per 

 month. Whence then this excess ? 



Mr. Fox (whose kindness to me in innumerable instances 

 has exceeded that of a parent) has in several cases detected 

 muriate of soda in water from some of the mines situated se- 

 veral miles from the sea, and thence remarks : " It may be in- 

 ferred from such facts as these, that the sea-water must in some 

 places penetrate into the fissures of the earth, and conse- 

 quently may in a greater or less degree assist in supplying the 

 loss of moisture carried off by evaporation^," &c. The slate 

 strata of Cornwall are usually considerably inclined, and the 

 veins by which they are traversed being unconformable to the 

 stratification, they must receive much of the water which per- 

 colates through the strata. 



* Meteorolog. Essays, p. 122. f Manchester Memoirs, O.S. v. p. 361,670. 



J Mr. Dalton's experiments on the evaporation from mould and vegeta- 

 tive surfaces, to which I have already referred, are the only ones on these 

 points which I have seen described in detail. If we follow the numbers 

 there given by this illustrious philosopher, it will give a different value to 

 the 8th and 10th columns of Table III. thus: 



cubic feet of water drawn, and evaporated more than the rain fallen ; and 

 when corrected for imperfection of apparatus, the excess still amounts to 

 59,881,580-54 cubic feet. The author has mentioned some of the objec- 

 tions to which his experiments are open. I shall therefore only remark 

 that they seem to need repetition. 

 Cornwall Geol. Trans, iii. p. 324. 



