78 SIXTH RKPORT 1836. 



GEOLOGY. 

 On certain points in Physical Geology. By Wm. Hopkins, F.G.S. 



Distinct approximations to general laws have long been recognised 

 in geological phzenomena connected with the dislocations of the crust 

 of the globe. In districts (as for instance our coal districts) where 

 faults abound, they usually consist of two systems, those in the one 

 meeting those in. the other nearly at right angles, the faults in each 

 system being approximately parallel. The same observation applies 

 to anticlinal and synclinal lines, and to longitudinal and transverse 

 valleys w^here they appear to be connected wdth lines of dislocation. 

 The directions of mineral veins present to us striking approximations 

 to the same laws ; and further, it is important to remark with respect 

 to all the phsenomena now mentioned, that when they occur in stratified 

 masses their directions are found to bear distinct relations to the dis- 

 turbed positions of such masses, one system coinciding with the direc- 

 tion of the strike, and the other with that of the dip of the beds. 

 Mineral veins also (or rather the fissures in which the matter propez'ly 

 constituting a mineral vein has been deposited) possess many characters 

 in common. Their depth is uniformly greater than that to which man 

 has been able to penetrate ; the most productive veins in stratified masses 

 are in the direction of the di]i, the cross-courses in that of the strike of 

 the beds, the latter being in general of considerably greater and much 

 more irregular width than the former. The corresponding beds in the 

 opposite walls of a vein are frequently at different elevations, thus 

 forming what is called the throw of the vein ; the planes of most veins 

 approximate to verticality ; insulated masses of the adjoining rock 

 (termed ridei's) are often found in them ; and finally, at their intersec- 

 tions they frequently present various appearances of relative displace- 

 ments. Trap and granite veins and horizontal beds of trap are also 

 phsenomena which must be regarded as associated with the elevatory 

 movements to which the crust of the globe may have been subjected. 



That the appearances of fracture in the earth's crust are not illusory, 

 but afi'brd certain indications of actual dislocation, it would appear im- 

 possible to doubt in the present state of geological inquiry ; and hence 

 we are naturally led to the inference that some dislocating force must 

 have acted beneath the fractured crust, and moreover that its action 

 must have been general and simultaneous, at least to the extent of the 

 districts throughout which the phcenomena follow the same laws without 

 breach of continuity. Assuming this to be the case, Mr. Hopkins's ob- 

 ject has been to institute an investigation, founded on mechanical and 

 physical principles, and conducted according to mathematical methods, 

 to ascertain how far the phcenomena above-mentioned are referrible to 

 the cause to which we have been led to assign them. 



The author makes no hypothesis in these investigations as to the 

 manner in which the elevatory force is produced ; he merely assumes 

 its simultaneous action under portions of the earth's crust of consider- 

 able extent. With respect to the constitution of the elevated mass in its 

 undisturbed state, it is sufficient for the strict applicability of his re- 



