CHAP. XXXVIII 
THE PLA TEA U OF SMALL ISLES 
225 
appears again at the base of the precipice overlain by prismatic basalts. 
But the conglomerate, here only 12 feet thick, is made of much finer 
detritus which, largely composed of volcanic material, includes small well- 
rounded and polished pebbles of Torridon Sandstone. Beneath it lies a bed 
of 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 being at the top of the sedi- 
mentary group, lies at the bottom. I was informed by Mr. A. Thom 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 a mile and a half still further 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 surface already referred to 
(p. 187). This band not improbably occupies the same platform as the 
upper conglomerate of Compass Hill. It is only about seven feet thick, the 
lower four feet consisting of a dull green pebbly tuft’ or ashy sandstone, with 
small rounded pieces of Torridon Sandstone, while the upper three feet are 
formed of dark shale with crowded but indistinct remains of plants. Here 
the more usual order iij the sequence of deposition is restored. The shale is 
indurated and shattery, so that no slabs can be extracted without the use of 
quarrying tools. 
Bather less than half a mile towards the south, on the roadside at the 
gully of Chi 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. 270. A remarkable slaggy basalt (a) rises into a hummock, against 
which have been deposited some fine granular tuff’s (b) whereof only a few 
inches are visible, that pass up into a thin band of dark shale (c), including 
a layer of pebbly ferruginous 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). Tt 
will be observed that this upper lava 
cuts Out the shale and thus comes to Fig. 270. — Section of shales and tuffs, witli a coni- 
whc-f 4. i ^ a ^ ferous stivm p lying between two basalt-sheets, 
lest directly upon the lower sheet. At cw liam M i4, Sanaa, 
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 five inches in height by three 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 
VOL. II Q 
