^Ol- 57 'J CRFSH-CONGLOMEEATES OF ARGYLLSHIRE. 323 



In the light of this evidence I revisited some of the sections in 

 the immediate neighbourhood which I had formerly regarded as 

 indicating contemporaneous erosion. 



About half a mile north-north-east of Balameanoch an epi- 

 diorite and gritty limestone are seen in juxtaposition. The former 

 rock on one side of the limestone is sufficiently fresh to leave no doubt 

 of its igneous origin, crystals of hornblende and felspar being easily 

 recognized, while on the other side of the limestone it occurs as a 

 vesicular, green, calcareous chlorite-schist, much decomposed : a type 

 of rock, as mentioned earlier (p. 318), into which these epidiorites 

 often merge, and extremely difficult to distinguish from similar rocks 

 of sedimentary origin. The limestone is conglomeratic, being studded 

 with grains of quartz and felspar which sometimes attain 1 inch in 

 length. In addition, however, we find numerous flattened boulders 

 derived from the adjoining calcareous chlorite-schist. When the 

 ground was mapped, the evidence furnished by these boulders led 

 me to regard the deposit as one of contemporaneous erosion, and 

 representative in this area of the Highland Boulder-bed. I was 

 likewise led to consider the calcareous chlorite-schist as a sediment : 

 for, being precluded by this interpretation from placing it with the 

 epidiorite- sills, the only other alternative was to regard it as an 

 altered lava or ash-bed, which the evidence over the district generally 

 did not support. 



On re-examining the ground last year it was apparent to me that 

 it was a repetition of the sections of crush- conglomerate that are 

 so readily formed at the junctions of the gritty limestone and epidi- 

 orites. A careful examination of the calcareous chlorite-schist 

 failed to reveal the smallest trace of recognizable clastic material. 

 Further, its homogeneous nature and the absence of any evidence 

 of the alternations of the material of deposit, pointed to its forming 

 a part of the big igneous sill of this district into which it appears 

 naturally to pass. 



Considering the comparative readiness with which this limestone 

 lends itself to the manufacture of crush-conglomerates I am inclined 

 to be doubtful in cases where this material has been regarded as 

 forming the matrix of boulder-beds, whether we are not dealing 

 with the former phenonemon. The time at my disposal in the 

 Highlands last season did not admit of my re-examining those 

 localities in the Loch Awe basin which I had instanced in my former 

 paper ^ as furnishing examples of the Highland Boulder-bed, but 

 provisionally it would be safer to regard those in which the matrix 

 is calcareous as crush-conglomerates. 



As stated earlier(p. 320), these phenomena, although mostprevalent 

 in the limestone audits junction with the epidiorite, are not confined 

 thereto. Near Creagantairbh similar structures are observed 

 in a band of fine quartzose rocks, which occupy a zone 5 or 6 feet in 

 thickness between coarse massive grits. Some of the quartzose rock 

 is very fine-grained and compact, having almost the appearance of 



1 Quart. Journ. Geol. ^oc. vol. Iv (1899) pp. 487-89. 



