Vol. 50.] ANNIVERSARY ADDRESS OF THE PRESIDENT. 95 



west, according to Messrs. Peach and Home, the formation has a 

 maximum thickness of about 1800 feet, in which they recognize 

 four subdivisions, including an angular basal breccia, which occurs 

 at any horizon where the domes of the generally level gneissic plat- 

 form project through the Torridonian deposits. Above this is a 

 conglomerate which presents features of special interest, as the com- 

 ponent pebbles have not been derived from the underlying gneiss. 

 These pebbles point to the existence of an older series of sedimentary 

 deposits and volcanic rocks (slaggy diabase-porphyrite), no trace of 

 which has yet been met with throughout the Archaean (in this case 

 Lewisian) area. Dr. Hicks, who generally has an eye to possible 

 Pebidians, noticed the occurrence of rocks foreign to the district in» 

 the Torridonian conglomerate of Ross-shire some years ago. The 

 formation thickens towards the south, attaining about 4000 feet in 

 Assynt, and even 8000 feet in the Loch Broom district, but the 

 distinctions observable in the north cannot here be made out. 

 Amidst masses of coarse sandstones, grits, and occasional bands 

 of conglomerate, are, in places, both high and low in the series,- 

 shaly beds with indications of organisms. Worm-casts are also 

 noticed in the upper beds, and quite low down in the series are 

 calcareous rods of an enigmatical character. 



I have been somewhat particular in giving the details of the 

 Torridon Sandstone, because of its well-defined position as a local 

 series, which may some day give rise to an independent system ;, 

 though this, perhaps, is expecting too much, when we bear in mind 

 how numerous are the claimants for the obscure and barren territory 

 between the Archaean and the fossiliferous Cambrian. The rocks 

 of Howth Hill and Bray Head, for instance, despite the claims of 

 Prof. Blake to place them in his Upper Monian, are still regarded by 

 Prof. Sollas as possibly of Cambrian age. 1 Referring to the occurrence 

 of organic remains in the quartzite of that district, he says that their 

 appearance so forcibly recalls that of the Cambrian in Sutherland, 

 that one instinctively looks for the worm-tubes of that region, and 

 though repeated search in the thick massive quartzite has failed to 

 reveal them, yet in certain of the thiuner beds similar markings 

 are far from rare. He refers to the discovery in a greenish quartzite, 

 a little south of Bray, of a number of large burrows with an ex- 

 panded trumpet-like opening 3 inches in diameter, and singularly 

 resembling the ' trumpet-pipes ' of Assynt. This is the Histioderma 

 hibernicum of Kinahan. Again, as Prof. Sollas observes, near the 



1 Proc. Geol. Assoc, vol. xiii. (1893) p. 94. 



