1850.] MURCHISON EARLIER VOLCANIC ROCKS OF ITALY. 309 



merely because the latter have somewhere been emitted from volcanic 

 vents, we should be forced to grant, that the formation of domes, 

 circuses, and valleys of elevation in sedimentary deposits of aqueous 

 origin, has not been occasioned by the action of plutonic heat or its 

 accompanjring gaseous forces. It is evident that the somewhere 

 whence the volcanic submarine detritus has been derived, may in 

 many cases be hundreds of miles distant from the deposit ; since no 

 one can limit the area to which currents will transport light scoria- 

 ceous and volcanic dejections. 



For my own part, however, I deem it to be impossible to examine 

 the most striking valleys of elevation in our own country, such as 

 Woolhope and the Dudley Hills, and see how the strata of limestone 

 in those beautiful ellipses are the more fissured by transverse cracks, 

 the more they have been strained and bent, and then observe that 

 such ellipses often run parallel to adjacent outbursts of plutonic rocks 

 which have broken up and thrown off' similar strata, and not be con- 

 vinced, that such examples do in some measure illustrate the point at 

 issue. Will any other explanation suffice to account for the shape 

 and fractures of the Wren's Nest and the ellipses near Dudley, except 

 that of intumescence due to the powers of heat connected with the 

 vast diffusion of plutonic matter in that tract ? I may be excused for 

 asking those English geologists, who may doubt the efficacy of the 

 interpolated igneous rocks to have produced these striking results, to 

 read the chapters I have written on the subject*, and afterwards 

 the memoir of Mr. Blackwell, of Dudley, which delineates the under- 

 ground play of the igneous matter, and shows how it has powerfully 

 fractured all the submarine strata and given to the Staffordshire coal- 

 field its form and outline. It is scarcely fair to argue against all craters 

 of elevation, because no plutonic or volcanic rocks have been observed 

 to form the central fulcrum of our English valleys of elevation. For, 

 in my mind, the very circumstance that such ellipsoids are so sym- 

 metrically eccentric in their dip, is the reason why we should not 

 expect to find any igneous rock within them. It is, I suggest, from 

 the repression of the effort of the heat, steam, and gases to escape 

 upwards along the axes of such ellipsoids of elevation, that their qua- 

 qua-versal arrangement is due. Nor must it be forgotten, that in the 

 very districts so affected, the igneous matter has usually sought an 

 issue (notably, for example, in the Rowley, Malvern, and Abberley 

 Hills) along the edges of the adjacent deposits, probably because it 

 there met with less resistance than in the neighbouring tracts, which 

 deposits have by the same causes been rolled into undulations, or 

 heaved up into rapid anticlinals. In numerous cases, however 

 (and the west flank of the Malvern is a good instance), we see that 

 the eruptive rock has performed the part of raising and even of over- 

 turning the strata on its flank. 



The observations I made in Italy, and which I again apologise for, 

 as being necessarily imperfect, have thus led me to add a few words 

 to what I have already written j- upon the subject, in the hope of mo- 



* See Silurian System, pp. 480, ef seq. 



t See Silurian System (Valley of Woolhope). 



