REVIEWS 287 
In chap. x, on the history of development of Jo Daviess County, 
the lead-zinc mining industry is recognized as the cause of the early 
settlement and development of the region. The rough topography and 
relatively thin and infertile soils of the Driftless Area make agriculture 
less profitable here than in the surrounding glaciated country. 
lel IRA 1B 
Geology of the Navajo Country. A Reconnatssance of Parts of 
Arizona, New Mexico, and Utah. By HERBERT E. GREGORY. 
U.S. Geological Survey, Professional Paper No. 93. 4to, 
pp. 161; maps. 
This useful. and valuable summary of Professor Gregory’s long 
studies of the Navajo country covers an area of more than twenty thou- 
sand square miles, a region inhabited almost exclusively by the Navajo, 
Hopi, and San Juan Indians. The report deals fully with the geography, 
stratigraphy, igneous rocks, structure, physiography, and economic 
geology of this little-known region, and is illustrated with numerous 
photographs and two pocket maps of the geography and geology. 
The sedimentary rocks, from the Pennsylvanian to the Eocene, with 
part of which at least the reviewer has some acquaintance, are treated 
extensively in their various subdivisions. The descriptions and illus- 
trations will serve as an excellent guide to the future explorer. Their 
correlation is in part one of peculiar difficulty because of the absence of 
characteristic fossils. Permian strata are identified with doubt. No 
fossil vertebrates have hitherto been discovered in this region, but the 
reviewer confidently believes that they will be in future, probably in 
the lower part of the Moenkopi and underlying formations. The strata 
referred to the De Chelly formation are certainly higher than the fossil- 
iferous Permian beds farther east, and might with equal propriety be 
called Lower Triassic. The Shinarump conglomerate, lying below 
Upper Triassic strata, as determined by their vertebrate fossils, is not 
only widespread throughout this region, but is identified with assurance 
by the present writer as far north as the Wind River Range in western 
Wyoming. It seems everywhere to be a reliable guide to the fossil- 
iferous Triassic beds immediately above it. The fossil-bearing Chinle 
beds of the Upper Triassic are doubtless equivalent in age to those called 
by the writer the Popo Agie beds some years ago. Their description is 
characteristic. 
