S 1 4 Geological Society, 



jacent hill or boss of hard rock, in which case the effect of upward 

 pressure might resemble that seen, on a small scale, in the paper of 

 a bound book, where a minute knob in one leaf has imparted its 

 shnpe to a great number of other leaves without piercing through 

 them*. Whatever hypothesis we favour, it is essential to observe 

 that such hills as the Wren's Nest near Dudley, and others of similar 

 ellipsoidal forms and internal structure, do not correspond to the 

 type of volcanic hills, such as Etna, Mount Dor, or the Cantal. In 

 both cases there may be an approach to a cone, and the beds may 

 dip everywhere outwards from a common centre; but, in the vol- 

 canic mountain, the beds having an outward dip, thin off as they 

 appro:ich the base or circumference of the cone, which is not the 

 case in inclined beds composing the hills alluded to in the neigh- 

 bourhood of Dudley : nor in the last-mentioned instances do the 

 lowest or subjacent rocks crop out round the circumference of the 

 cone, as happens in the instance of the volcanic eminences before 

 alluded to, where the granite of the country round Mount Dor, the 

 fresh-water beds and mica schist in the Cantal, the marine deposits 

 around Mount Etna in Sicily, — each appe^ar at the surface as soon 

 as we have left the slope of the cone, and advance upon the sur- 

 rounding low country. 



In attempting to explain the principal transverse faults of tlie 

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

 principles expounded by Mr. Hopkins in his Researches in Piiysical 

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

 the Cambridge Philosophical Societyf. 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 phaenomena ; 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 acertain depth, is expanded by heat so as to elevate 



• Dr. Fitton, Geol. Trans. 2nd Series, vol. iv. p. 244. 



t [Mr. Hopkins's " Abstract of a Memoir on Physical Geology ; with a 

 further Exposition of certain points connected with the subject," appeared in 

 Lond. and Edinb. Phil. Mag., vol. viii. p. 227. et seq. A discussion also of 

 certain parts of the suhject, by Dr. Boase and Mr. Hopkins, will be found 

 in vol.ix. pp. 4, 14, and 171, et seq. — Edit.] 



