498 Notices of Memoirs — Sir A. Gexkie — N. W. Highlands. 



respects the same, lie was evidently inclined to class the whole of 

 these genera under one generic denomination, despite their marked 

 and manifold external differences. In his Sil. Suppl. p. 95, he says : 

 " It will remain a question for further consideration whether we are 

 justified in retaining the three generic denominations of Nudeospira, 

 Retzia, and Meristina, for shells possessing the same simple loop." 

 It is therefore in agreement with the principles of classification 

 adopted by Davidson that I now place the species which Sowerby 

 named Iceviuscula under the genus Bifida, of which Bifida lepida is 

 the type. 



P.S. — Davidson's Sil. Suppl. was issued in two portions in the 

 Annual volumes of the Palasontographical Society for 1882 and 1883. 

 After writing the above article I have found in the Index accom- 

 panying the latter portion of the Suppl. that Davidson ultimately had 

 the same doubts as myself as to the true generic position of Icevius- 

 cula. In the Index referred to — Sil. Suppl. p. 233 — Davidson puts 

 a note of interrogation to the generic name of Athyris as applied to 

 IcEviiisciiJa, and he adds concerning Athyris, — " It is not certain 

 whether we possess any true British Silurian species of the genus." 



Abstracts of Papers read before Section C. at British Asso- 

 ciation Meeting, Cardiff, August, 1891. 



I. — Discovery of the Olenellus-zonb in the North-west High- 

 lands. By Sir Archibald Geikie, F.E.S., Director-General of 

 the Geological Survey. 



EVER since the Geological Survey began the detailed investigation 

 of the structure of the North-west Highlands of Scotland the 

 attention of its officers has been continuously given to the detection 

 of any fossil evidence that would more clearly fix the geological 

 horizons of the various sedimentary formations which overlie the 

 Lewisian gneiss. A large collection of organic remains has been 

 made from the Durness Limestone, but it has not yet yielded mate- 

 rials for a satisfactory stratigraphical correlation. The study of this 

 collection, however, has confirmed and extended Salter's original 

 sagacious inference that the fauna of the Durness Limestone shows 

 a marked North American facies, though, according to our present 

 terminology, we place this fauna in the Cambrian rather than in the 

 Silurian system. Below the Durness Limestone lies the dolomitic 

 and calcareous shaly group known as the ' Fucoid beds,' which, 

 though crowded with worm -castings, has hitherto proved singularly 

 devoid of other recognizable organic remains. In following this 

 group southwards through the Dundbnnell Forest, in the west of 

 Eoss-shire, my colleague, Mr. John Home, found that, a few feet 

 below where its upper limit is marked by the persistent band of 

 ' Serpulite grit,' it iucludes a zone of blue or almost black shales, 

 During a recent visit to him on his ground, when he pointed out to 



