TRANSACTIONS OF SECTION C. 1031 
moraines, composed of granitic gravel and sand. At Tormsdale a vein of some 
einder-like material occurs. The flagstones at Poll a’ Chreagan are covered with 
freestone, as also at Dale Bridge on the right bank of the river. On the left the 
flags lie exposed in great tabular masses, overlying limestone. At the top of the 
Mill Poolare the remains of a natural dam. Below this pool a band of freestone 
once crossed the bed of the river. At Dale are shifting beds of gravel, and here the 
river is continually changing its course. Below Pollihour flags again appear, and 
opposite Scots Calder are banks of boulder clay, the boulders therein being very 
distinctly striated. Great masses of flagstone block up the bed of the stream 
at Gerston. At Halkirk the cliffs are coated with red ochre. 
Granite is not visible at Dorrery, as has been stated by at least one writer, but 
it does not appear to lie at any great depth below the flags. 
At Achanarras a curious fossil Coccostews is found in a small slate quarry. 
East from Spittal the angle at which the rocks dip gradually diminishes, and 
at Lanergill reaches its nearest approach to a dead level. 
Drift gravel prevails in the neighbourhood of Halsary, and also down part of 
Strathbeg, where the banlis of the ancient river may again be traced. Here the 
Dalmore moraines are continued. 
No evidence of volcanic action can be gathered from an examination of the rocks 
of Central Caithness, but the district presents a fair field for the study of erosion by 
ice, air, and water. 
8. Onsome Rock Specimens from the Islands of the Fernando Noronha Group. 
By Professor A. Renarp, LL.D., F.G.S. 
The rock specimens described in this communication were collected by J. G, 
Buchanan, Esq., during the voyage of the ‘Challenger.’ The islands have been 
described by Darwin in his ‘Geological Observations on Volcanic Islands’ (2nd 
edit., p. 27), The author, after having explained the geological structure, gave 
lithological descriptions of the chief types of the rocks, which may he referred to 
the phonolites (St. Michael’s Mount). ‘These phonolites are composed of sanidine, 
augite, nepheline, hornblende, magnetite, nosean, and titanite. 
The rocks of Rat Island are basalts with nepheline. The constituent minerals 
are augite and olivine. The ground-mass is almost entirely composed of nepheline ; 
biotite and apatite occur as-accessory constituents. The little island known as 
Platform Island is also basaltic, with a doleritic texture. It is composed of labra- 
dorite, augite, olivine, magnetite, and biotite. This rock has undergone altera- 
tions. 
9. On the Average Density of Meteorites compared with that of the Harth.' 
By the Rev. H. Hits, M.A., F.G.8, 
The average density of the meteorites which fal] on the earth is attempted to be 
calculated. Different methods described give as results 4:55, 4°58, 4:84, 5°71; the 
last value being influenced by the size of one particularly large metallic specimen, 
‘The average density of the earth is usually regarded as 5°6. Meteorites are samples 
of the materials of space, and a mass of them would aggregate into a body of density 
not widely differing from that of the earth. The densities of the other planets are 
not inconsistent with a like origin. Consequently any theory of the genesis of the 
earth from pre-existing materials involves a probability that an important part of 
its nucleus is metallic, 
1 Geological Magazine, 1885, p. 516. 
