1888-89.] The Duke of Argyll on Bodies of Organic Origin. 63 
now brought under the notice of the Society have a direct and imme- 
diate bearing. That question relates to the movements effected in 
these strata, subsequent to their induration, by subterranean causes. 
More than thirty-five years ago, before any special controversy had 
arisen on the comparative effects of atmospheric denudation, and of 
subterranean movement on the structure of our mountains in the west 
of Scotland, I had been led by the facts presented in our intrusive 
rocks, especially by our porphyries, to conclude that these masses had 
risen along the planes of deposition among the sedimentary series, 
and that their intrusion among these was contemporaneous with a 
falling in of the sedimentary beds along certain lines of weakness, 
due to weight from under which support had been withdrawn. 
Such a movement of falling in, or tumbling down, along lines of 
consequent depression, would necessarily be accompanied by the 
slipping and sliding of the falling beds over each other along the 
of planes sedimentation. This conclusion I communicated in a 
paper to the Geological Society of London so long ago as 1853.* 
It is, therefore, no surprise to me to find that these bodies, whether 
they be worm-casts, as I now confidently believe, or whether they be 
purely mineral in their origin, prove conclusively that the rocks in 
which they are found have been sheared — or have slipped — over 
each other by movements due to subterranean causes. I am not 
myself able to conceive how mineral concretions, such as iron pyrites, 
or clay balls, or any other form of purely mineral aggregation, could 
have been so formed as, when pulled out and sheared, to present 
the uniformly ovate, or semi-ovate sections, together with the purely 
linear tube-like forms presented to us in these specimens. But if this 
be the explanation of them, the shearing must have been very great. 
On my own interpretation of an organic origin, some shearing, and 
squeezing, and elongation of the worm-casts is equally admitted. I 
see no evidence, indeed, that our hills about Inveraray have been 
ever exposed to such tremendous earth movements of horizontal dis- 
placement as those which have recently been revealed in Sutherland. 
But I have long been satisfied that the forms of our Highland 
mountains are due mainly to subterranean subsidences, with contem- 
poraneous issue of plutonic and intrusive rocks; and the appearances 
in the quartzite now described and exhibited are, on any conceivable 
* Quart. Jour. Gcol. Soc. of London, November 1853. 
