2 Mr HOPKINS, ON RESEARCHES IN PHYSICAL GEOLOGY. 



which the phenomena are observed to approximate, without interruption 

 to the same geometrical laws. Between these phenomena and their 

 actual causes necessary relations must of course exist; and in this 

 paper I purpose to examine how far such relations do exist between 

 our observed phenomena and a certain general cause to which they 

 may be attributed. But in the first place it will be necessary to state 

 distinctly the nature of the phenomena to which I refer, though with- 

 out entering into more detail than may be necessary for my immediate 

 object. 



I. Faults. 



a. In districts where faults abound, two distinct systems are usually 

 found, in each of which the faults approximate to parallelism* with each 

 other. 



/3. The common direction of one of these systems is approximately 

 perpendicular to that of the other. 



y. The plane in which the dislocation at a fault has taken place is 

 frequently somewhat inclined to the vertical ; and it appears that the 

 side of the fault on which the strata are most elevated, is more fre- 

 quently that toivards which the plane of dislocation inclines ^o/« a ver- 

 tical through the lowest point of a section of the fault, by a vertical 

 plane transverse to the plane of dislocation f. 



II. Mineral Veins. 



A distinct idea of a mineral vein is perhaps most easily formed by 

 conceiving a vertical fissure, varying in width from a few inches to a 

 few feet, to have been formed, extending downwards from the surface, 

 and to have been subsequently filled up with matter in the midst of 

 which the ore which properly constitutes the mineral veinl is deposited, 



* This term must in certain cases be taken in a modified sense, as will be explained 

 hereafter, whatever may be the phenomena to which it is applied. 



+ See Encyclopedia Metropolitana, Art, Geology, p. 541. 



X This is termed by miners in the Northern districts a Rake-Fein. In Cornwall the 

 whole substance contained in the fissure is called a Lode. 



