UNITED STATES, CANADA AND MEXICO                        57 consists in building large fires against the base of the rock which becomes heated, whereupon water is thrown over it. The sud­den change of temperature cracks off large pieces, and much of the turquoise is ruined in the process. After cracking off the rock, the turquoise is picked out of the exposed seams with pieces of pointed iron, such as old harrow-teeth, or any other sharp-pointed instrument. Only occasionally is there a blast put in. The turquoise is sold in Santa Fe, or along the line of the rail­road in the vicinity of the mines, by the Indians of the San Domingo pueblo, N. M. The specimens are ground into round or heart-shaped ornaments, which are pierced with a crude form of bow-drill, called by them " malakates." The drilling point is either quartz or agate, and the wheel to give velocity was in one instance made of the bottom of a cup. The selling price of the ornaments is now very low, the Indians disposing of their speci­mens at the rate of twenty-five cents for the contents of a mouth, where they usually carry them. A string made up of many hun­dreds of stones, they value at the price of a pony. Comparatively little of the American turquoise finds sale except as cabinet specimens, or as mementos of travel. Still, for ornamental or in­laying work, were it properly introduced, it might have a large sale, as the green and blue-green tints would contrast favorably with many stones or with dark wood. It is possible that deeper workings will develop finer stones, perhaps of such material as will maintain a more permanent color. Concerning the origin of the turquoise veiningrock, both Prof. John S. Newberry and Prof. Benjamin Silliman, Jr., regard it as eruptive. According to Prof. Frank W. Clarke, the very small size of the veins and their limited distribution show that the turquoise is of local origin, and he em­phasizes the idea that it has resulted from the alteration of some other mineral. In addition to the facts tending to show its deriva­tion from apatite, there is also the fact that epidote containing lime is present as a secondary product. The existence of the pyrite in the gold-bearing veins may have had something to do with initiating the process of alteration, and the alumina of the turquoise was probably derived from decomposing feldspar. Dur­ing the summer of 1885 a very full suite of specimens was col­lected by Maj. John W. Powell, and placed for analysis in the