ARGYLL INVERARY DISTRICT. 363 



as to the possible cause of such an association of these two rocks, 

 there is one preUminary question which must be either settled by 

 proof, or passed over as not really admitting of any serious doubt ; 

 I mean the question of the sedimentary origin of the mica-slates. On 

 this point I can only say, that there appears to me to be every proof 

 except one — the remains of organic life. Nothing can be more com- 

 plete and regular than the stratification of these rocks ; and if there 

 be any other mode whereby such a mechanical arrangement of earthy 

 matter can be effected than that of aqueous deposition, it is a mode 

 of which we have no knowledge. There are the same alternations. 



Fig. 2. — Ideal Section of the Inverary District. 



Mica-slate, 



which prevail in all other sedimentary rocks, of siliceous, shaly, and 

 calcareous beds ; and in respect to the latter, I have had the benefit 

 of examining some limestone strata in this district, along with Sir 

 Roderick Murchison, which were pronounced by him to be not very 

 much more crystalline than some of the limestones of the older rock's 

 which are so abundant in their oceanic fossils. 



The absence of organic remains, however, is of course no real 

 stumbling-block in the way of our conclusion, as it is perfectly con- 

 sistent with our knowledge of actual facts, that such remains, if they 

 ever existed, may well have been obliterated by metamorphic action ; 

 and further, because it is equally consistent with theories having at 

 least some probability, that in these very ancient rocks we should find 

 evidences of a period anterior to the introduction of organized beings 

 to our planet. 



Taking for granted then the sedimentary origin of the mica-slates, 

 and therefore the comparative horizontality of their first position, it 

 becomes a question of much geological interest, how they came to 

 assume such a highly inclined position, and how such masses of in- 

 trusive igneous rock came to be interposed between their beds, with- 

 out interrupting their general conform ability of dip and of direction ; 

 the igneous and the aqueous rocks assuming the position, as it were, 

 of contemporaneous formations. 



With igneous rocks of another class, this is no unknown phseno- 

 menon ; sheets of trap or lava interposed between the beds of sediment- 

 ary rocks are not unfrequent ; and a remarkable example has been 

 brought under the notice of this Society by Professor E. Forbes, in 

 reference to the oolites of Skye. But the cause of such a conjunction 



