ing this interestin 
a at uj ‘y o . yh 
\ 3 ‘ : Bet 
T. 8. Hunt—The Decay of Rocks. SBE 
College, in whose company I lately had an opportunity of visit- 
g locality, published in 1880 a geological 
He 
which escaped this action. 
9. Turning now to the valley of the Mississippi, we find 
that Pumpelly in his geological survey of Missouri, showed in 
1873 that the decay im situ of granitic rocks and of quartzifer- 
ous porphyry has left great rounded blocks of these crystal- 
line rocks, while the conversion of the porphyry into clay, an 
Its subsequent removal, has liberated included veins or masses 
iting hematite, giving rise to an accumulation of detri- 
dito as 
340. Proceeding from Missouri northward, we find that in 
Minnesota, as shown by,C. A. White" in 1870, and by N. H. 
Winchell in 1874, the ancient granitoid rocks, when protected 
Mr. E. T Sweet, which have been already referred to, § 16. 
Further details of the same region and its kaolins, with analy- o . 
Ses as before, were given by Irving in an essay in 1880 on the = 
* Annals New York Acad. Sciences, vol. ii, part 6. ‘ 
* Geology of Missouri; Report on Iron Ores and Coal Fields, pp. 8-12. _ 
Secon: 
and Geol, Essays, p. 250. 
*+ Trans, Wisconsin Academy, etc., iii, 13. 
