334 HE. G. BAEEOAV ON THE OCCUEEENCE OP [Aug. I9OI, 



repeated by rapid folding, though it is quite possible that some true 

 basic lavas may also be present. The crushed and decomposed acid 

 rock near Brawliemuir ma}', as already suggested, have been 

 originally a lava. It must, however, be borne in mind that, owing 

 largely to repetition by folding, no rock much below the horizon of 

 the jasper is ever exposed. 



The succession of the rocks in these lenticular patches that inter- 

 vene locally between the Highland Schists and the Old Red Sandstone 

 is tabulated below in descending order: — 



fl. Grey shale. 



2. Pebbly liinestone, lenticular, 1 to 5 (?) feet thick ; quarried at all known 

 outcrops. 



3. Dark carbonaceous, grej-, chocolate-coloured, and white shales ; about 20 

 ■{ feet thick. 



4. Pebbly grits, with carbonate-of-iron cement, becoming coarser towards 

 tile base ; about 120 feet thick in the North Esk section. 



5. Green conglomerate, occurring locally about 30 feet thick in the North 

 \^ Esk section. 



fl. Fine grit with microcline-pebbles. 



2. Fine shale, always cleaved, with a pseudocrystalline aspect. 



3. Jasper (altered radiolarian chert ?), 6 feet thick in the Noi-th Esk 

 g i 5 -( section; at certain localities it seems to be replaced by jaspery 



phyllite. 



4. Green Rocks, mainly lenticular sills of ophitic dolerite, though 

 l^ some lava-flows may also be present ; upper part only visible. 



s 



O 



cri 



9 « 



is o 



no H OQ 



III. The Age op the Two Series. 



Attention has already been drawn to the local character of the 

 deposits forming the Margie Series. The nature of the chert and 

 fine shale associated with it points on the other hand to oceanic 

 conditions of sedimentation, and suggests a wide distribution. 



When I had completed the survey of the North Esk region, a 

 series of uncrushed specimens and a section showing the geological 

 structure of the area were examined by Mr. Peach, who at once 

 recognized the resemblance of the Jasper and Green-Rock Series to 

 the radiolarian cherts and volcanic rocks of Arenig age in the 

 Southern Uxjlands, and the similarity of the geological relations in 

 the two regions. Subsequently, most of the sections in the North 

 Esk region were visited by Mr. Home, who was equally impressed 

 with the resemblance in the field, notwithstanding the deformation 

 of the rocks along the Highland Border. 



At a later date Mr. Peach and Mr. Home showed me certain 

 typical sections of the radiolarian chert and Arenig igneous rocks in 

 the neighbourhood of Sanquhar, where the junction between the two 

 is of two distinct types. In the first, the chert rests on an uneven 

 surface of the pillowy lava, cracks and fissures in the latter being filled 

 by chert: no similar junction has j'et been detected along that por- 

 tion of the Highland Border which I have examined. In the second 

 type, the junction of the chert and igneous rock is perfectly even, and 

 resembles that seen in the northern area of Forfarshire andXincar- 

 dineshiie. In the latter region, the mechanical deformation which 



