1888-89.] The Duke of Argyll on Bodies of Organic Origin. 61 
often confined to some one bed, hardly more than a few inches thick 
— proving that the conditions under which organisms have been 
preserved in rocks are peculiar and are often absent. The same 
lesson may be learned from the Cambrian sandstones, underlying 
this quartzite in the Northern Highlands, in which we find abundant 
ripple-marks, but no trace of life. In this case, of course, we are 
not absolutely certain that life existed at all in the area, and at the 
time, of the deposit of the sandstones. But as regards the mica- 
slate series in Argyllshire, the indications of marine sedimentation 
are quite as decisive, and so far as this conclusion is concerned, the 
discovery of marine organic remains is by no means required. 
Neither, in my opinion, are they needed to confirm the geological 
horizon of Silurian age to which our metamorphic rocks in the 
South-Western Highlands have been long presumably assigned. As 
regards Argyllshire, at least, this presumption rests upon evidence 
far more direct than the conjecture of Murchison, that our rocks 
represent the southward prolongation of the beds which have yielded 
in Sutherland fossils of ascertained Lower Silurian type, and which 
are there found above the Cambrians on the west and below the Old 
Red Sandstones on the east. That conjecture was, I believe, a true 
one, and the general facts on which it rested remain unshaken. But 
the evidence for the Silurian horizon of the mica slates, schists, and 
quartzites of Argyllshire, is much more direct than the evidence in 
respect to the same rocks as developed farther north or in the 
central Grampians. All round our Argyllshire coasts we have 
patches and fragments left of the same Old Red conglomerates and 
sandstones, which are faulted against the south-eastern flanks of the 
Grampians, from the Clyde to Stonehaven. These patches and 
fragments of the Old Red are everywhere seen to lie, or to have 
lain, over and upon the upturned beds of the metamorphic series. 
In some places they have remained in considerable mass, and 
include thick beds of limestone as well as of freestone. This is 
the case on the coast of Kintyre, from the harbour of Campbelltown 
to Southend, near the Mull of Kintyre. The limestones of the Old 
Red in that district have been highly silicified, and so far as yet 
observed all organic remains have been obliterated. But these lime- 
stones with associated beds of freestone have their geological horizon 
determined in Kintyre by the direct evidence of dipping under the 
