362 



SIR A. GEIKIE ON THE TERTIARY 



[May 1896, 



dark shale, with remains of plants, resting immediately on a zeolitic 

 amygdaloid which plunges into the sea. The chief interest of this 

 locality is to he found in the shale which, instead of appearing at 

 the top of the sedimentary stratification, lies at the bottom. I was 

 informed by Mr. A. Thorn that leaves had been obtained from this 

 shale, but I was not successful in my search for them. The locality 

 is only accessible by boat, and, as the coast is fully exposed to the 

 Atlantic swell, landing at the place is usually difficult and often 

 impossible. 



About 1J mile still farther west, where a foreshore fronts the 

 precipice of Earnagream at the Camas Tharbernish, a band of 

 intercalated sedimentary material underlies the great escarpment 

 of basalts and rests upon the slaggy sheet with the singular ' aa ' 

 surface already referred to. This band not improbably occupies the 

 same platform as the upper conglomerate of Compass Hill. It is 

 only about 7 feet thick, the lower 4 feet consisting of a dull green 

 pebbly tuff or ashy sandstone, with small rounded pieces of Torridon 

 Sandstone, while the upper 3 feet are formed of dark shale with 

 crowded but indistinct remains of plants. Here the more usual 

 order in the sequence of deposition is restored. The shale is in- 

 durated and shattery, so that no slabs can be extracted without the 

 use of quarrying-tools. 



Bather less than J mile towards the south, on the roadside at 

 the gully of Cul nam Marbh, the basalts enclose a sedimentary 

 interstratification which not improbably lies on the same horizon as 

 those just described along the northern shore. The relations of the 

 rocks at this locality are shown in fig. 17. A remarkably slaggy 

 basalt (a) rises into a 



hummock against which Fig. 17. — Section of shales, tuffs, and a 

 have been deposited some coniferous stump lying between two 



fine granular tuffs (b), basalt-sheets. Cul nam Marbh, Canna. 



whereof only a few 

 inches are visible, that 

 pass up into a thin band 

 of dark shale (c), includ- 

 ing a layer of pebbly fer- 

 ruginous tuff, with small 

 rounded pea-like pieces 

 of basalt, basic pumice, 



bole, limonite, etc. At the top of this shale an irregular parting of 

 coaly material (d) lies immediately under the slaggy base of the 

 succeeding basalt (e). It will be observed that this upper lava cuts 

 out the shale and thus comes to rest directly upon the lower sheet. 

 At the point where it begins to descend it has caught up and enclosed 

 a small tree-stump (d') which stands upright on the coaly parting 

 and shale. This stump, at the time of my visit, measured 5 inches 

 in height by 3 inches in breadth ; it had been thoroughly charred 

 and was crumbling away on exposure, but among the pieces which 

 I took from it sufficient trace of structure can be detected with the 

 microscope to show the tree to have been a conifer. 





