REVIEWS 44s 
Detailed descriptions, with maps and analyses, of the exposures of Trenton lime- 
stone are given in the final chapter of the report. Certain limestones of higher horizons 
are also discussed in this connection, as are the deposits of white shell marls. 
Lee, H. A. Mineral Resources of Colorado — Larimer County Gypsum. 
Stone, Vol. XXI, pp. 35-37, 1900. 
Larimer county is the largest gypsum producer in Colorado. The gypsum depos- 
its are associated with rocks of Jura-Cretaceous age, and occur in a basin between 
rocky ridges. The main quarry is operating ona knoll showing a face of gypsum 
250 feet long, and 28 feet high in the middle, thinning to 7 feet at the edges. The 
gypsum is quite compact and gray in color. The amount of stripping does not exceed 
18 inches. The material is blasted out, auger holes being bored to receive the charge 
of explosive. 
The mill of the Consolidated Plaster Co. has a capacity of 40 tons per day of 
ten hours. It is built on a side hill and the gypsum is received from wagons at the 
top of the mill, fed through coarse and fine crushers, and then over screens to buhr- ; 
stone mills. From these it is carried to five-ton kettles, two and a half hours being 
consumed in charging, “boiling,” and discharging. No details are given concerning 
the retarders used. 
McCatuiz, S. W. Preliminary Report on the Roads and Road-Butlding 
Material of Georgia. Bulletin 8, Georgia Geol. Surv., 8vo, pp. 264, 
Pls. 1-27, Figs. 1-28, geologic map, 1901. 
The chapters of this bulletin fall naturally into three groups, treating respect- 
ively the subjects of road construction in general; the topography and geology of 
Georgia in relation toroad construction and road building materials ; and the methods 
of road making in the various counties of the state. The first of these groups includes 
chapters on the history of road construction; the value of good roads; the theory of 
road making, as regards locations, grades, and surfaces; the maintenance and repair 
of roads; the considerations governing the selection of road materials ; and the tools 
and machines used in highway construction. These chapters furnish an excellent sum- 
mary of the general subject of road making. 
In the second group fall chapters on the topography of Georgia in its relation to 
the highways, and on the road-building materials of Georgia. A colored map shows 
the areas covered by the crystalline, the Palaeozoic, and the Cretaceous and Tertiary 
rocks; and the location of the trap-dykes which occur in the crystalline area. 
The Palzeozoic area is divided topographically, following Hayes, into the plateau, 
sharp ridge and valley region. The plateaus have a level surface, but terminate in 
steep escarpments. Owing to the steepness of these escarpments, it is difficult to carry 
a road by easy grades from the valleys to a plateau, but when the elevated areas are 
reached the cost of construction is slight. The plateaus also affect road work by act- 
ing as barriers to free communication between their bordering valleys. The second 
type of surface consists of a number of sharp, parallel ridges, trending northeast and 
southwest, and due to the weathering of the upturned edges of hard sandstone (which, 
in the plateau region, lies almost horizontal). The smaller ridges are frequently inter- 
