Page:A Treatise on Geology, volume 2.djvu/198

 184 Mr. Kenwood, in his communication to the Geological Society (Nov. 1832), mentions several instances of remarkable intersections, some of which are, and others are not, easily explicable by the supposition of real movements in right lines.

Thus, if, "in Weeth mine, two cross courses are traversed by the same east and west lode, and one is heaved to the left, and the other to the right" (in a horizontal plane,) this would necessarily happen if the cross courses dipped in contrary directions, and the movement on the plane of dislocation were vertical. In all such cases, precise and complete measures are necessary, to enable a candid inquirer to form a satisfactory opinion as to the mechanical solution of the problem of displacements involved in the data; and such a case Mr. Kenwood presented to the Section of the British Association at Liverpool. Most of the phenomena described in that communication were capable of explanation by simple movements in right lines, but some were not; particularly the case of two veins, dipping in opposite directions, and yet heaved the same way, contrary to the mechanical necessity of the case, had the movement been real. In such cases, angular movements of the masses, which are known, by examples of common faults, to be real causes, may be appealed to.

It is impossible now to enter into a minute examination of this and other such cases of embarrassment, which change their aspect when a whole district of related veins is submitted to consideration; but having examined many of the published examples of intersection of veins in Cornwall, it is our opinion at present that much of the difficulty has arisen from the incomplete description of the phenomena, and the division of the general problems belonging to a considerable extent of displaced ground, into a multitude of minor cases, the key to which is in their connection. There can be no doubt that the great mass of these phenomena are perfectly reconcileable with the hypothesis of real displacement of the masses of rock, and it appears to us