ei 
Review of Hall and Whitney's Geology of Iowa. 115 
for hydraulic lime are those from the Buff limestone, at the k 
of the Trenton. It remains to be ascertained, by practical trials, 
atmosphere. Some samples give as much as fifteen per cent of 
‘ ur 
yTites an 
Value of western coals. No workable iron-ore of any import- 
ea has been discovered in connection with the coal-measures of 
owa, which are exceedingly thin, no section pai been meas- 
ae the Des Moines valley giving much over a hundred feet 
lekness, 
Sj The Subject of the occurrence of the lead ore in the Lower 
ilurian limestones of the Upper Mississippi valley, and, espe- 
cially, within the limits of Iowa, is discussed in this megert on 
Pages 422 to 468, The rincipal crevices, or lead ng 
tes, Which have been worked in the vicinity of Dubuque 
are described, and a diagram given illustrating their surface- 
