Geological Society. 47 



and by pointing out with equal fidelity all those districts which come 

 within the application of his theory, as well as those great metal- 

 liferous tracts, in which as yet no trace of contiguous, unstratified 

 rock has been observed. Why are we to shrink from the supposition, 

 that in this, as in the production of other phenomena, nature may 

 not have employed various means, when it is known that a distin- 

 guished French chemist *, imitating her energies, has succeeded in 

 producing simple minerals by the direct union of their constituents. 

 If, therefore, the ingenuity of a second Hall should demonstrate the 

 very manner in which volcanic forces, under great pressure, may 

 have produced effects analogous to those of sublimation beneath 

 the common atmosphere, there are still wide fields for experiment. 

 For who can venture to expound all the possible effects of those 

 changes depending upon the laws of electro-magnetism, which must 

 have been evolved by the varied actions of the elements, brought 

 into play during those movements by which the land and sea have 

 changed their places ? 



In the mean time, the Essay of M. Necker must be regarded as an 

 excellent stimulant to research} and judging from my own limited 

 experience, and particularly from facts observed in the mining dis- 

 tricts of the west of Shropshire during the last summer, I should infer, 

 that England will not be found deficient in phenomena amply corrobo- 

 rative of the views of Humboldt, Bou6, and Necker. — Mr. Henwood has 

 long been engaged in an inquiry, the objects of which cannot be too 

 much commended ; and you have already heard the result of a con- 

 siderable number of his most laborious investigations. It would appear 

 from these that he has already ascertained that the phenomena of the 

 mineral veins of Cornwall, do not come under those general laws to 

 which they have been referred by the native miners. As, however, 

 his labours are still in progress, it would be premature to speak of 

 the consequences to which they point, before the whole of them are 

 given to the public. 



I am here naturally led to speak of a work upon the Geology of 

 Cornwall, by Dr. Boase, composed of two parts, the former of which 

 contains most instructive and valuable detail, collected with inde- 

 fatigable industry, and is a most important addition to our previous 

 knowledge of the structure of that portion of our island. The Second 

 Part, though supported by arguments conducted with skill, and tending 

 consistently to one leading object, is directly opposed to the opinions 

 of nearly all modern geologists. Dr. Boase differs from previous ob- 

 servers, who conceived that certain granitic veins which ramify through 

 the slates have been injected into the latter -, and supposes, since many 

 of these veins are made up of the same ingredients as the surrounding 

 slate, that the whole is of common and contemporaneous origin, the 

 veins being merely crystalline segregations. Now, without denying 

 the existence of many contemporaneous and segregated veins in 

 Cornwall as in other countries, surely no one can at this day resist 

 the accumulated mass of evidence adduced by Allan, Sedgwick, 



* Berthier. 



