1 6 Dr. Boase's Additional Remarlcs on 



there can be no doubt then that all future dislocations must 

 aflect a basis of solid rocks possessing lines of structure, and 

 therefore would be subject to the modifying circumstances 

 which Mr. Hopkins is desirous of evading. 



In opposition to this statement, can Mr. Hopkins adduce 

 any evidence in support of his conjecture, that various degrees 

 of solidification existed in all the rocks subjected to elevatory 

 movements? If not, the convenience alone of his hypothesis 

 ought not to be admitted as a sufficient argument ; and my 

 deduction from facts cannot be considered as satisfactorily 

 answered by treating it as ^' a priori reasoning founded on what 

 we are alto^jether ignorant of." 



In order to illustrate the subject more fully, let us direct 

 our attention to the principal movements which Cornwall is 

 supposed to have undergone. These appear to be referrible 

 to four periods, marked by — 



1st. The protrusion of the granite through the stratified 

 rocks, tilting them up at various angles, and injecting granite 

 in the form of veins into the adjacent fissures. 



2nd. The formation of porphyritic dykes or elvan-courses 

 which traverse both the granite and the slate. 



3rd. The production of metalliferous veins, intersecting the 

 granite, slate, and elvans ; and, 



41 h. The introduction of another system of veins, traversing 

 all the preceding formations, locally termed cross-courses. 



1. What was the condition of the stratified rocks, when 

 the first and most remote movement occurred ? Could it 

 have been at the lowest degree of solidification, or indeed, at 

 any degree short of absolute solidity? I think not. 1st, Be- 

 cause, admitting that process to have been " the gradual work 

 of lengthened periods of time," we have a very sufficient limit 

 in the countless ages which must have elapsed between the 

 deposition of the non-fossiliferous strata of Cornwall and 

 the formation of the carboniferous or the saliferous group, 

 whichever may be determined to mark the period when the 

 granite was protruded. 2ndly, Because the nature of the de- 

 tritus derived from the older strata, and contained in the con- 

 glomerates formed before the elevation of the granite, indicate 

 that the parent rocks must have been in a solid state. And 

 lastly, because the sharp angular portions of slate, included 

 within the granite veins, demonstrate that they could not have 

 been forcibly detached from rocks only partially solid. Thus 

 ^then we see that even iii limine Mr. Hopkins has great diffi- 



Ities to contend with, in refusing to admit the perfect solidity 

 ^oftlic inferior disturbed strata; and these must necessarily 

 be ii^^ased at each successive step. But before advancing 



iQ^aseu 



