THE 
AMERICAN GEOLOGIST. 
Vol. XXVII. MARCH, 1901. No. 3. 
SOME NOTES ON THE TRAP DIKES OF GEORGIA. 
By S. W. McCaI-LIE, Atlanta, Ga. 
Plates XII-XIV. 
The trap dikes of Georgia are confined to what is known as 
the Crystalhne area, an old land surface, occupying the central 
and northern part of the state. This area is made up largely 
of schists and gneisses with numerous intrusive bosses of 
granite. The schists and gneisses occur chiefly in alternate 
bands or zones having a northeast-soutlnvest trend. The 
dikes are pretty evenly distributed throughout the area and 
are found mostly in groups which consist of one large, or 
mother dike, paralleled on one or both sides by smaller dikes. 
The larger dikes often attain a maximum width of 200 
feet and sometimes extend for many miles with but few in- 
terruptions. A good example of one of the larger dikes is 
to be seen in a cut on the Central railroad, a few miles cast of 
Newnan in Coweta county. This dike continues for about 
sixty-five miles in a southern direction through Coweta, Meri- 
wether and Talbot counties, finally disappearing beneath the 
Columbia sands some four miles south of Talbotton. Within 
this distance there occur a few breaks or interruptions a mile 
or more in length due either to an actual discontinuity of the 
dike or its burial beneath the residual products derived from 
the enclosing schists. 
The smaller dikes vary from an inch to a yard or more in 
width and never continue for more than a few hundred rods. 
In some localities these smaller dikes are quite numerous. On 
the Georgia railroad near Covington as many as seven of these 
dikes are to be seen within a short distance of each other. Tlie 
