44 
Proceedings of Royal Society of Edinburgh. [sess. 
of Scotland. It was only in examining a very small island, called 
Garvh, lying about one mile off the nearest shores of the Bay of 
Durness, — an island hardly belonging to the Hebridean group at all, 
and really a mere fragment of the Sutherland Mainland, that he was 
led to observe the fossiliferous strata at Durness and Eriboll.* And 
here we come upon the curious fact, that although quartzite rocks of 
great thickness occur far to the south of the remarkable develop- 
ments of it in Sutherland and Ross-shire, and although Macculloch 
did not fail to identify it elsewhere as the same rock, both mineralogi- 
cally and stratigraphically, yet out of the classical region where it is 
so conspicuous it ceases altogether to exhibit the same rod-like bodies 
and “ vermicular forms ” which Macculloch did observe at one spot, 
and of which he spoke so doubtfully. It has long now been the 
accepted interpretation by all geologists that these bodies represent 
the tubes or burrows made by marine worms of many species in 
the intertidal zone of shores of the sea. This interpretation is not 
without its difficulties of detail. We are all familiar with the 
appearance of worm-castings on our sandy and muddy shores ; 
and more attentive observers must have sometimes been surprised 
by the immense numbers of these burrowing annelids in particular 
areas. But the natural supposition would seem to be that although 
each one of these worms must make a tube in the sand or in the mud 
in which it feeds and burrows, yet these tubes must be as evanescent 
as the passage of the annelid, because the pressure of wet sand on 
its own particles, or the transferring and transfusing effects of water 
permeating its substance, would seem to be causes sure to effect a 
rapid obliteration of any temporary vacuity made by the passage of 
the worm. Still it is certain that internal tubes and passages must 
be made by such worms in the course of their ceaseless operations, 
and that they must be made in enormous numbers when the sand 
or the mud, or a combination of both, is sufficiently charged with 
organic matter, to support the annelids in such abundance as we 
constantly see upon the shore. It is perfectly natural, therefore, 
that upon primeval shores on which fine sand was constantly being 
formed and deposited during periods of time which were more or 
less prolonged, worms should have burrowed as they burrow now, if 
this form of organic life had been at that time established. The 
* Maccullocli’s Western Islands, vol. ii. p. 508. 
