accomplished by Sorby, Zirkel and Rosenbush may be attributed to the introduction of thin sections of rocks for microscopical analysis. These sections are ground thin enough to allow the use of transmitted light, and although but a small slice of a rock be examined, it reveals their composing minerals and their structure and also their accessory aggregates.

The structure and means of cementing of rocks is clearly represented in the various sections made in various directions.

The base of a rock is by aid of the polariscope readily decyphered, whether it be crystalline or amorphous. The base of porphyry is composed of minute particles of feldspar and quartz. Basalt was found to contain sometimes enclosures of a glassy character, which in many cases are so large that they assume the aspect of a base through which the crystalline part is scattered, and rocks which were always considered as amorphous, were shown by aid of thin sections to be in a state of crystalline formation.

One of the most interesting features of lithology is the chapter treating of the cause and result of metamorphic changes in rock. A section of an altered rock presents in itself the whole story of a process which for a long series of years must have been working to produce a chemical and physical alteration in those solid bodies. We learn by the study of the thin section with the microscope, which of the composing minerals was at first disturbed and changed, and how the progress of change in the molecules was gradually spread through the whole mass. The well-known rock, serpentine, may illustrate this. A section presents outlines of crystals which are on the borders serpentine, but which in their centre enclose a clear and unaltered nucleus of chrysolite, the remainder of the chrysolite crystal, the form of which is preserved in serpentine. Further, basalt carries chrysolite as one of its most common accessory minerals. Nearly all these chrysolites are in a state of metamorphism, their outlines showing bands of serpentine, similar in structure to the serpentine occurring in large masses and the origin of which has been found to be in a compound rock changing by the chemical and physical alteration to a homogeneous one.

A careful microscopical study of rocks and minerals of a country enables us also to trace the original rocks which furnished those immense layers of drift clay, which when prepared for the

microscope appears as a mass of debris of rocks altered by mechanical means and pseudomorphical actions.

The study of thin sections of rocks has also widened our knowledge of the more frequent occurrence of certain minerals as micro-mineralogical accessories, as magnetite, menaccanite, apatite, hornblende, tourmaline, nepheline, nosean, microlites, and many others.

It is also due to microscopical researches that crystallography and mineralogy have been abundantly enriched in facts which may be of the greatest importance for their development as sciences. What we formerly thought to be a single crystal has shown itself as a number of crystals in position of twin formation. A great number of crystals, principally quartz, have been found to be porous, the pores filled with liquid, most likely water and carbonic acid, and these pores are the most frequent if quartz occurs in granite or syenite.

Orthoclase presents under the polariscope two systems of bands crossing each other at right angles. Labradorite is filled with menaccanite and magnetite; and mica and magnetite generally pierced with apatites when occurring in granites, or in diorites.

It is not the intention of the writer to describe all those results of micro-lithological researches which within a few years have reorganized lithology and richly contributed to geology, mineralogy and crystallography. The remarkable work of Prof. Zirkel, forming the sixth volume of the Report of the United States Geological Exploration of the Fortieth Parallel, under the direction of Prof. Clarence King, Geologist-in-charge, will demonstrate at once the importance of thin section in lithological researches.

Palæontology likewise has derived a great many new facts, as will be seen in a forthcoming volume of the "Palæontology of the State of New York," by Prof. James Hall. A great number of sections of corals and sponges and other fossils have been prepared and illustrated. The result derived from its perusal will show that palæontology also has progressed as much as lithology by the adoption of thin sections and the microscope as a means for the study of fossils.

VOL. XIL-NO. 1.

IT

THE SPRINGS OF SOUTHERN NEVADA.

BY D. A. LYLE, U. S. A.

T is the intention of the writer to merely jot down a few personal recollections of some of the springs visited in the arid region of Southern Nevada, while a member of one of the Wheeler expeditions.

To those who have experienced the pangs of thirst, while journeying over the desolate wastes that characterize this section, it will not be surprising that reminiscences of water should linger longest in the memory of the traveler. In fact the procurement of that necessity is a matter of such vital importance that all movements are subordinated and controlled by the answer to

the question, "Is there any water there?" Should the reply be in the negative, some other route must be followed, or else a supply of water must be carried along. The springs in this portion of the Great Basin are few, and often far between. Their waters differ much in quantity, temperature and chemical composition. In quantity, the yield varies from a few gallons per day to a never failing supply. As to temperature, the heat of the waters range through cold, cool, tepid and warm to boiling. As regards chemical composition, some are fresh, others alkaline, and still others, sulphurous. In the waters of some springs, a mere trace of saline ingredients are found, while in other cases the salts are present in sufficient quantity to produce saturation.

The first that will be mentioned are Mud Springs (Fig. 1), also

known as Desert Wells, from the fact that parties passing that way, have dug pits from four to eight feet deep when there, in search of more water. These springs, when visited by the writer, were mere pools of muddy slime, with a slight film of stagnant water overlying the viscous blue marsh. So nauseous were these waters that neither men nor animals could drink them. Enough water, however, was obtained by digging new pits or "wells" near by, to partially alleviate the sufferings of man and beast, which were somewhat intense after marching over thirty miles through the heated sands of the Smoky Valley Desert upon a July day.

These springs-if springs they may be called-were situated at the southern extremity of Smoky Valley surrounded by a dreary waste of sand and "alkali flats," with here and there a stunted sage bush.

Day break the following morning found the party en route to Silver Peak, the next objective point. Silver Peak, a small mining camp, is located near the west side of Clayton Valley, and at the eastern base of the Red Mountain range. Near this place and along the western border of the salt marsh which forms the major part of the basin are the Thermal Springs. The more important ones are eleven in number. With one exception they are contained in a narrow belt, running almost north and south. This belt is about a half mile in length, its width being but a few rods. Beginning at the southern limit of this line, the first spring we encounter is in a small depression in the general surface. (Fig. 2.) Its waters are slightly saline, but quite palatable, and are the best for use in the vicinity. The

temperature of the water is 69° Fahr. Just north of this is found a cluster of springs; the largest and most central one is called Saturn. (Fig. 3.) Their temperatures are 69.5° Fahr. These springs are in close proximity to each other, and flow out upon a level area some twenty acres in extent, covered with a rank growth of coarse salt grass, from whence the water flows into the salt marsh.

Proceeding northward, we next meet with three salt springs arranged in the form of an isosceles triangle, differing widely in temperature and the degree of their saturation.

These are situated in the edge of the salt marsh, the two forming the base, being in an east and west line, twenty feet apart. The more westerly one has a temperature of 79° Fahr., while the other one in its quiescent state has a temperature of 117.8° Fahr., and at irregular intervals boils and emits steam. The third,

Fig & Saturn Spring

forming the apex of the triangle and lying ninety feet north, has a temperature of 116.5° Fahr.

Still further north are two more salt springs, situated also in an east and west line, only four feet apart; the westerly one, as before, having the lowest temperature, being 79° Fahr., while the other has a temperature of 117° Fahr. Another spring (Fig. 4). about one fourth of a mile north of the others, was constantly boiling and emitting steam. A gurgling noise could be heard in several places near the main opening, under the tufaceous crust of calcareous matter deposited by its waters. In approaching this spring the greatest caution had to be exercised to avoid breaking through the crust of tufa which bridged and in part, concealed the seething waters, which could be seen through the many perforations in this treacherous envelope. Every step in