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Comparing the rocks of Trans-Pecos Texas with those of acknowledged mining districts of America and Europe, their similarity, and in many instances the identity of character, can not be disputed.

The influence of the enclosing rocks upon the ore bearing and the character of the inclosed veins is also an undisputed fact; and whatever theories of the formation of ore veins may be advanced, one thing seems to be true, viz., that the fissure veins as well as contact veins derived their ores directly or indirectly from depths not yet reached by mining.

The study of ore deposits, the conditions under which the veins were filled with ores, the causes of their formation, are and will be for some time to come a matter of speculation and conjecture.

Though this knowledge from a practical standpoint is of the greatest value, it seems with most geological observers and writers of secondary importance, no doubt partly on account of the greater difficulty to make conclusive observations.

The actual observations are confined in most cases to mines. There they must be made under an illumination to which (with the exception of practical miners and mining experts) only few observers are used; the field of observation is limited, and the connection of the surface phenomena with those in the mines are few, partly covered by timbering, and