446 REVIEWS 
sected by streams along whose valleys cross country roads of easy grade can be con- 
structed, while the main roads are located in the valleys, which offer no serious obstacle 
to construction. The valley region consists of low, wide, comparatively level valleys, 
in which highway construction is simple. 
The crystalline area is divided into two regions—the mountainous and the 
plateau. The former consists of rugged peaks separated by narrow valleys, in which 
flow rapid streams; and road construction and maintenance is difficult and expensive. 
In the plateau region highway construction is easy, as light grades can be obtained, 
and the cost of grading is slight owing to the deep decomposition of the underlying 
rocks. 
The Tertiary area is a plain, sloping gently southward, and traversed by large 
streams. Swamps and depressions along stream valleys offer the only serious obstacles 
to road construction which, except in these places, is very inexpensive. 
The road materials occurring in the Palzeozoic area are limestones, cherts, shales, 
and sandstones. The limestones of the area are abundant and well suited for road- 
metal. They are allof the Silurian age, and occur in three different formations; the 
Knox dolomite, the Chickamauga limestone and the Bangor limestone. Of these the 
first is the most important, owing to its thickness and arealextent. It is easily quarried 
and crushed and furnished excellent road metal. Some beds of the Chickamauga for- 
mation supply good material, as does the Bangor limestone. ‘The areal extent of this 
last formation is, however, too small to make it of importance. 
The Palzeozic cherts are widely distributed and extensively used. They occur in 
both the Knox dolomite and the Fort Payne chert. The material is well suited to 
roads of light traffic, but inferior to limestone where the traffic is heavy. It binds well 
but becomes dusty in dry weather. The chert is often located favorably for working 
and transportation. 
The shales and sandstones of the Palzeozoic are locally used, but are not satisfac- 
rory material. 
In the crystalline area the rocks available for road work are granite, gneiss, dio- 
tite, trap schist, quartzite, and marble. Of these the last three are unsatisfactory as 
road metals. The granites, and the less well-laminated gneisses and diorites, furnish 
fair macadam. The trap dikes which are widely distributed in the crystalline area» 
furnish excellent material. These diabases are dark gray to black, fine grained, and 
very tough. At present this material is little used, but will probably become impor- 
tant. 
The Tertiary area supplies limestone, buhrstone, and gravel. The limestones 
consist of shell fragments, with some sand, in a calcareous matrix. They have been 
used extensively in southern Georgia, and are very satisfactory, cementing readily 
jnto a compact, hard surface, comparatively free from dust. Buhrstone is of little use. 
The gravels cemented by ferruginous clays make durable and very satisfactory roads, 
and are largely used. 
Nevius, J.N. Roofing Slate Quarries of Washington County, New York. 
Nineteenth Rept. N. Y. State Geologist. Pp. 135-150, Pls. 26-37, Igol. 
Gives detailed descriptions of the slate quarries and quarry methods and a dis- 
cussion of the general features and condition of the industry. The working quarries 
