2 Proceedings of the Royal Physical Society. 



The special subject to wliich I wish to direct your attention 

 this evening is one of great interest and importance to 

 geologists — viz., the light shed by organic remains on the 

 history of the strata in which they are embedded. For the 

 elucidation of this subject I propose to select several illustra- 

 tions from the geology of Scotland with which I am familiar. 



For the last few years I have been engaged in the study of 

 the Silurian rocks of the North- west Highlands, so closely 

 linked with the famous controversy of the age of the crystal- 

 line schists of the Highlands. As these are the oldest strata 

 from which fossils have been obtained in Scotland, it may 

 not be inappropriate to place them in the foreground. The 

 basement beds of the Silurian rocks of Sutherland and Eoss 

 consist of coarse-grain-ed, false-bedded grits or quartzites, 

 resting on a remarkably even plane of marine denudation 

 carved out of Archaean gneiss and the overlying Cambrian 

 conglomerates and sandstones. There is therefore a marked 

 unconformability between the Silurian strata on the one 

 hand and the Archaean and Cambrian rocks on the other. 

 No organic remains have yet been detected in this lower 

 division of the quartzite series, w^hich attains a thickness of 

 about 200 feet. Overlying this subdivision we find about 

 300 feet of comparatively fine-grained quartzites, which, wdth 

 certain exceptions, are characterised by much more regular 

 bedding. Almost every bed is pierced by a series of vertical 

 cylinders or " pipes," varying in diameter from -| to 3 or 4 

 inches, not distributed equally throughout the group, but 

 arranged in definite order — each variety being confined to 

 certain bands. As a rule, these cylinders become more 

 numerous towards the top of the quartzite series. There can 

 be no doubt whatever that the " pipes " are due to the con- 

 solidated casts of burrowing annelides. Next in order, we 

 find the "Fucoid beds," about 50 feet of grey shaly bands, 

 with lenticular masses of dolomitic limestone and occasional 

 flaggy grits — the whole series weathering with a brown 

 ochreous tint from the presence of ferruginous matter. The 

 shales are traversed along the bedding planes by flattened 

 worm casts, which have been mistaken for fucoids, and 

 hence the name that has been misapplied to the group. 



