487 



In attempting to explain the principal transverse fiiults of the 

 Dudley coal-field, Mr.Murchison refers frequently to the theoretical 

 principles expounded by Mr. Hopkins in his Researches in Physical 

 Geology, a paper printed in the 6th volume of the Transactions of 

 the Cambridge Philosophical Society. Mr. Hopkins has there en- 

 deavoured to develop, by reasoning founded on mechanical prin- 

 ciples, and by mathematical methods, the effects of an elevatory 

 force acting simultaneously at every point, beneath extensive por- 

 tions of the crust of the earth. He is aware that in nature such a 

 force must usually act under complicated conditions, so as to pro- 

 duce irregular phsenomena ; but he observes that in order to have 

 a clear conception of the manner in which it would operate in pro- 

 ducing movements and dislocations, it is useful to assume certain 

 simple conditions to which mathematical investigations may be 

 applied. When we have deduced in this manner some results free 

 from all uncertainty, these may serve as standard cases to which the 

 geologist may refer more complex problems. Thus for example, 

 a portion of the earth's crust may be assumed to be of indefinite 

 length, of uniform depth, and bounded laterally by two vertical par- 

 allel planes, beyond which the disturbing force does not extend. 

 It is then supposed that a quantity of subterranean vapour or melted 

 rock, existing at a certain depth, is expanded by heat so as to elevate 

 the superincumbent mass, the resulting fissures in this mass may then 

 become matters of calculation. According to Mr. Hopkins, recti- 

 linear lines of dislocation will give rise to a set of longitudinal pa- 

 rallel fissures, and simultaneously to others precisely at right angles 

 to them ; whereas in conical elevations, the fissures will divei-ge 

 from a centre. If the general axis of elevation be curvilinear, the 

 longitudinal fissures preserving their parallelism with it will be also 

 curvilinear, while the transverse fissures being perpendicular to the 

 former at their points of intersection will no longer be parallel. 



To return from this digression, I must now recall your attention 

 to other papers relating to the carboniferous deposits of England. 

 The coal-measures of the north-western coast of Cumberland have 

 been examined by Prof. Sedgwick and Mr. Williamson Peile, who 

 have described the Whitehaven and other fields in great detail, il- 

 lustrating their account with a map and sections. The recorded 



