ARGYLL — INVERARY DISTRICT. 365 



right angles with the planes of stratification ; and wherever such a 

 force was exerted with success, those strata must have been violently 

 broken and disturbed, as is so frequently the case elsewhere around 

 the flanks of granitic hills. 



To account for the phsenomena which have been described, we 

 must suppose the intrusive force to have acted under such conditions 

 as regards the slates, that the planes of their stratification presented 

 to that force the lines of least resistance. 



No doubt there are conditions under which the planes of stratifi- 

 cation would be also the planes of least resistance to liquid matter 

 acting from below, although they had not lost their original horizon- 

 tality, — conditions such as those already referred to, under which trap, 

 rising through perpendicular fissures, is afterwards spread out late- 

 rally in sheets, either between, or on the top of, sedimentary strata. 

 But I have already pointed out certain considerations which go far 

 to show that such conditions are not applicable to the case before us ; 

 first, in respect of the difference between such sheets of trap and the 

 irregular masses of granite ; secondly, in respect of the difficulty of 

 accounting in the latter case for the parallel position of the slates and 

 granites being retained through changes during which the original 

 horizontality was lost. 



The situation of these rocks can be best explained, as it appears to 

 me, if we adopt a supposition which it is the object of this paper to 

 suggest to the Society, and which is also, I thmk, most reconcileable 

 with the other phsenomena of the district. 



I account for the granitic masses occupying the position they now 

 do in respect of the inclined strata of mica-slate, by supposing that 

 the failing in of the mica-slates from an horizontal to an inclined po- 

 sition, and the rise of the granites along the loosened planes of strati- 

 fication, were connected and simultaneous events. Such a falling in 

 of the stratified rocks would have at once the effect of loosening the 

 adhesion of their mutual surfaces, of causing them to slide off, open 

 out, or otherwise separate from each other, and of forcing up the 

 melted granites into which they fell. The present relative position 

 of the sedimentary and igneous rocks, as if they were of contempora- 

 neous origin, would be thus explained. Contemporaneous as regards 

 origin, I have endeavoured to show they cannot be ; but contempora- 

 neous they really are, on the supposition above made, as regards their 

 present relative position ; inasmuch as the same movement which 

 sunk the one, brought the other up to light. 



It seems to me that one of the main features, not merely of the 

 granitic district of Loch Fyneside, but, as before observed, of the 

 greater part of the county, greatly tends to strengthen this suppo- 

 sition ; I mean the prevalence of one direction of dip over extensive 

 areas of country, pointing to some general cause operative over a 

 wider field, and with greater equality of effect, than the mere local 

 upheaval of eruptive rocks. Generally, where we have the uptilting 

 of sedimentary rocks unequivocally due to such eruptions, we have 

 evidence of repeated movements more or less of a local character, 

 producing frequent changes of direction as well as of degrees of inch- 



