PRESIDENTIAL ADDRESS. } 449 
The Torridonian strata were evidently accumulated under desert or’ con- 
tinental conditions, and could therefore furnish little or no evidence bearing upon 
the development of marine life. That life existed, however, is clear from the 
presence of phosphatic nodules, containing remains of cells and fibres of organic 
origin, in the upper division of the system, and from the presence of worm 
burrows and casts in the Diabaig beds (Lower Torridon). 
Geologists are familiar with the fact that the Cambrian faunas all over the 
globe present highly specialised types belonging to most of the great groups of 
marine invertebrate life. Scotland is no exception to this general rule. For 
the fossils prove that their ancestors must have had a long history in pre- 
Cambrian time. 
The Cambrian Fauna of Scotiand. 
Beginning with the false-bedded quartzites forming the basal subdivision 
of the Cambrian strata in the North-West Highlands, we find no traces of 
organic remains in them, except at one locality, where worm casts (Scolithus 
linearis) were obtained. In the upper subdivision of the quartzites—the pipe- 
rocks—the cylinders of sand are so numerous that the beds have been arranged 
in five subzones, based on a definite order of succession of different forms 
probably of specific value. One of them, Arenicolites of Salter, may be of 
generic importance. Worms of this habit are confined to comparatively shallow 
water, and therefore near the shore line. Their occurrence helps to confirm the 
belief that the quartzites were laid down on an ancient shelving shore line during 
a period of gentle subsidence. Their presence also indicates the existence of 
plankton, from which they derived nourishment. Besides the relics of these 
burrowing annelids, one of the subzones of the pipe-rock has yielded specimens 
of Salterella (Serpulites Maccullochii)—a tubicolar annelid, which becomes more 
abundant in the overlying fucoid beds, serpulite grit, and basal limestone, where 
it is associated with Olenellus and other typical Lower Cambrian forms. 
The fucoid beds, which immediately overlie the pipe-rocks, consist chiefly 
of shales and brown dolomitic bands, with intercalations of grit locally developed. 
this type of sedimentation indicates that the mud line was superimposed on the 
shore line by subsidence. With this change of conditions there is a change of 
organisms, for though the burrowing forms (Scolithus) are still to be found in the 
sandy layers, the most characteristic types are those occurring along the bedding 
planes, known under the name of Planolites (Nicholson). They are very 
varied forms, and were probably produced by many types of errant annelids. 
The tubicolar annelids are represented by Salterclla, Coleoloides, and Hyolithes 
—an organism which perhaps links the worms with the hingeless brachiopods. 
This suggestion gains additional support from the researches of Dr. Walcott in 
the Middle Cambrian rocks of Canada. It is interesting to note that small 
annelids seem to have bored the spines of dead trilobites. Walcott has found 
similar borings in the chet of annelids in the Middle Cambrian rocks of 
Canada.* 
The researches of Dr. Walcott have proved beyond doubt that representatives 
of nearly all the divisions of the annelids are entombed in the Middle Cam- 
brian rocks of Mount Stephen, in British Columbia. We may therefore reason- 
ably infer that the worm casts of Scolithus type found in the North-West High. 
lands are due to annelids. He has also shown that worm-like holothurians are to 
be found in the same beds.* In this connection it may be observed that some 
of the recent holothurians have much the same habit of obtaining nourishment 
from the sands and silts containing organic matter. 
Fragments showing the characteristic microscopic structures of the plates 
and ossicles of echinoderms have been found in the fucoid beds. These are 
probably Cystidean. Hingeless forms of brachiopods also occur, among which 
may be mentioned Paterina labradorica and Acrothele subsidua. The type of 
Acrothele suggests a genetic descent from such a tubicolar worm as Hyolithes. 
Of the gasteropods, only one specimen, belonging to a subgenus of Murchisonia, 
has been obtained at one locality in Skye. Aelenia bella, a curved calcareous 
tube, open at both ends, doubtfully referred to the Dentalid« by Walcott, is 
comparatively plentiful. It occurs also in the Olenellus zone in Newfoundland. 
* Smuthsonian Miscell. Collect., vol. 57, No. 5, p. 125, 1911. 
* Itid., No. 8, 1911. 
1912. = 
