1881. 15 Trans. N. Y. Ac. Set: 
angles, and applicable in using the binocular camera for the purpose 
of taking slightly dissimilar pictures of the same object. He adds, (°) 
“when the optic axes are parallel, in strictness there should be no 
difference between the pictures presented to each eye, and in this case 
there should be no binocular relief; but I find that an excellent effect 
is produced, when the axes are nearly parallel, by pictures taken at an 
inclination of 7° or 8°, and even a difference of 16° or 17° has no 
decidedly bad effect. There is a peculiarity in such images worthy of 
remark ; although the optic axes are parallel, or nearly so, the image 
does not appear to be referred to the distance we should, from this 
circumstance, suppose it to be, but it is perceived to be much nearer.” 
This would not have seemed anomalous to Wheatstone, had he sup- 
posed binocular vision possible with divergence of visual lines, and 
entered into an analysis of the resulting visual phenomena. This 
analysis will be given in a future paper. 
Oct. 31, 1881. 
GENERAL SECTION. 
The President, Dr. J. S. NEWBERRY, in the Chair. 
Twenty persons present. 
The following paper was read by Mr. JoHN H. FurMAN: 
“THE GEOLOGY OF THE COPPER REGION OF NORTHERN TEXAS 
AND THE INDIAN TERRITORY.” 
The well-marked cretaceous beds of Parker County, Texas, extend 
for 30 miles north of west from Weatherford, on the road to Graham. 
They consist of strata of shelly limestone, sandstone and shaly clay, the 
latter grayish or reddish in color. An occasional thin seam of soft coal 
is found; and the water is strongly impregnated with lime. A stratum 
of sandstone stretches for thirty miles N. W. from Fort Worth. In this 
rock springs are found containing sodic carbonate, similar to the waters 
of the artesian wells of Fort Worth, Tarrant County, at a depth of 
about 270 feet. Towards Graham, the country assumes a semi-moun- 
tainous appearance, and, for twenty-five miles or more, sandstone ridges 
alternate with prairies, the hills being covered with scrub oak. Some of 
the ridges attain an elevation of two or three hundred feet above the 
prairies. The strata are horizontal, and large portions of the original 
surface have been carried away by erosion. The upper stratum is in 
many places a conglomerate, made up of small pebbles. In this region 
the seams of coal met with are generally soft, and the only workable 
(®) Idem, p. 514. 
