1 88 1. 15 Trans. N. Y. Ac. Scu 



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 y*' or 2>°, 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. 



