In the Star District of Southern Utah the country rock is Palaeozoic limestone, and it is cut by so great a number and variety of mineral veins that from the Harrisburg, a central location, a rifle shot would reach ten openings, all on as many distinct and different veins (viz., the Argus, Little Bilk, Clean Sweep, Mountaineer, St. Louis, Xenia, Brant, Kannarrah, Central, and Wateree).  The nearest trap rock is half a mile or more distant, a columnar dike perhaps fifteen feet in thickness, cutting the limestone vertically.  On either side of this dike is a vein from one to three feet in thickness, of white quartz with specks of ore.  Where did that quartz come from?  From the limestone?  But the limestone contains very little silica, and is apparently of normal composition quite up to the vein.  From the trap?  This is compact, sonorous basalt, apparently unchanged; and that could not have supplied the silica without complete decomposition.

I should rather say from silica bearing hot waters that flowed up along the sides of the trap, depositing there, as in the numerous and varied veins of the vicinity, mineral matters brought from a zone of solution far below.

To summarize the conclusions reached in this discussion.  I may repeat that the results of all recent as well as earlier observations has been to convince me that Richthofen’s theory of the filling of the Comstock lode is the true one, and that the example and demonstration of the formation of mineral veins furnished by the Steamboat Springs is not only satisfactory, but typical.

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[NATURE.]

HABITS OF BURROWING CRAYFISHES IN THE UNITED STATES.

On May 13, 1883, I chanced to enter a meadow a few miles above Washington, on the Virginia side of the Potomac, at the head of a small stream emptying into the river.  It was between two hills, at an elevation of 100 feet above the Potomac, and about a mile from the river.  Here I saw many clayey mounds covering burrows scattered over the ground irregularly both upon the banks of the stream and in the adjacent meadow, even as far as ten yards from the bed of the brook.  My curiosity was aroused, and I explored several of the holes, finding in each a good-sized crayfish, which Prof.  Walter Faxon identified as Cambarus diogenes, Girard (C. obesus, Hagen), otherwise known as the burrowing crayfish.  I afterward visited the locality several times, collecting specimens of the mounds and crayfishes, which are now in the United States National Museum, and making observations.

At that time of the year the stream was receding, and the meadow was beginning to dry.  At a period not over a month previous, the meadows, at least as far from the stream as the burrows were found, had been covered with water.  Those burrows near the stream were less than six inches deep, and there was a gradual increase in depth as the distance from the stream became greater.  Moreover, the holes farthest from the stream were in nearly every case covered by a mound, while those nearer had either a very small chimney or none at all, and subsequent visits proved that at that time of year the mounds were just being constructed, for each time I revisited the place the mounds were more numerous.