Remarks on Br. Boast's Primary Geology. 559 



" Lastly, the prevailing theory embraces igneous convulsions, as 

 one of its leading principles ; by which the stratified rocks are said 

 to have been forced up from their original horizontal position, and 

 inclined at various angles, by which they have been curved and 

 contorted ; and by which they have also been rent and fissured 

 in various directions : thus affording space for the intrusion of 

 igneous rocks, in the forms of veins or dykes, and for the formation 

 of mineral and metallic veins ; and also occasioning those faults and 

 dislocations so common both in the stratified and unstratified rocks. 

 To this doctrine, also, we cannot give our assent in toto. No one 

 can deny, that volcanic fires have in former times occasioned, and 

 still continue to produce, great mechanical alterations in the struc- 

 ture of the solid crust of our planet; but it does not appear to 

 be satisfactorily demonstrated, that the inclination of the primary 

 strata is attributable to this cause ; nor, that the phenomena of 

 granitic veins and dykes, and of metalliferous veins, are infallible 

 indications of igneous convulsions. 



"These are grave and weighty points of dissent, as regards the 

 stability of the Plutonic theory ; and, if we can only succeed in the 

 first instance, in giving plausible reasons for this difference of opi- 

 nion, the objections ought surely to receive a candid and patient 

 examination : they may be satisfactorily answered, or they may, 

 perchance, prove knotty and stubborn opponents. In either case, it 

 may be requisite to make appeals to nature by additional investi- 

 gations : so that there is some satisfaction in thinking, that, in 

 whichever way this discussion may terminate, by thus digging about 

 and examining the ground of the radical doctrines of the science, 

 the field of geology, like that of the departed husbandman in Bacon's 

 fable, may be rendered more fertile and productive. 



" In conducting the proposed enquiry, it is intended to arrange 

 it under the following heads : — 



" 1. Are the primary schistose rocks stratified ? 



" 2. Have the primary schistose rocks been elevated into* their 

 present inclined positions by Plutonic agency ? 



" 3. Are the primary schistose rocks sedimentary deposits, altered 

 by the contact of igneous rocks ? 



" 4. Do the primary rocks afford physical evidence that they have 

 experienced fissures, dislocations, and other mechanical movements ? 



