Address by Professor B. N. Peach. 457 



The researches of Dr. Walcott have proved beyond doubt that repre- 

 sentatives of nearly all the divisions of the Annelids are entombed in the 

 Middle Cambrian rocks of Mount Stephen, in British Columbia. We 

 may therefore reasonably infer that the worm casts of Scolithus type 

 found in the North- West Highlands are due to Annelids. He has also 

 shown that worm-like Holothurians are to be found in the same beds.-' 

 In this connexion 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 Eohinoderms have been found in the fucoid beds. 

 These are probably Cystidean. Hingeless forms of Brachiopods also 

 occur, among which may be mentioned Paterina labradorlca an(^ 

 Acrothele subsidua. The type of Acrothele suggests a genetic descent 

 from such a tubioolar worm as Hyolithes. Of the Gasteropods, only one 

 specimen, belonging to a sub-genus of 3Iurchisonia, has been obtained at 

 one locality in Skye. Helenia bella, a curved calcareous tube, open 

 at both ends, doubtfully referred to the Dentalidse by Walcott, is 

 comparatively plentiful. It occurs also in the Olenellus zone in 

 Newfoundland . 



But the organic remains that render the fucoid beds of exceptional 

 interest and importance are the Trilobites, because they clearly define 

 the horizon of this zone in the Cambrian system and display strong 

 affinities with American types. They are represented by five species 

 and varieties of Olenellus, very closely resembling the forms in the 

 Greorgian terrane, or Olenellus zone, on the east and west sides of 

 the North American continent. The genus Olenelloides has also been 

 recorded from these beds. The Crustacea are represented by Phyllocarids, 

 among which we find Aristozoe rotundata, likewise characteristic of the 

 Olenellus zone of North America. 



Next in order comes the serpulite grit, which indicates a recrudescence 

 of the pipe-rock conditions of deposition, and presents the Scolithus 

 type of Annelid borings. From the diameter of the pipe and the depth 

 of the burrow it is probable that the worm Itnay have belonged to 

 a different species from any of those whose casts are to be found in 

 lower horizons. This large variety is associated with smaller and more 

 irregular worm, casts which have often weathered out and leave the 

 rock honeycombed with hollow casts. The characteristic form from, 

 which the zone takes its name is Salter ella {Serpulites Maccullochii) . 

 It occurs abundantly along certain calcareous layers that mark pauses 

 in the deposition of the sand. This calcareous type culminates at 

 the top of the zone, where there is a thick, carious, weathering band, 

 crowded with specimens of Salterella, forming a passage bed into the 

 calcareous shales at the base of the Durness dolomites. At one locality 

 near Loch an Nid, Dundonnell Forest, Ross-shire, thin shales, inter- 

 calated in the serpulite grit, yielded a fine carapace of Olenellus 

 Lapivorthi — a form of frequent occurrence in the underlying fucoid 

 beds. Professor Lapworth recorded the finding of OrtJioceras and 

 linguloid shells in the top part of this zone at EireboU." 



Immediately above the serpulite grit in EireboU and Assynt we find 

 a few feet of dark calcareous shale, with iron pyrites, probably 

 deposited at the limit of sedimentation. This layer, which is singularly 

 devoid of organisms, ushers in the great succession of dolomites and 

 limestones, upwards of 1,500 feet in thickness — ^perhaps the most 

 remarkable type of sedimentation among the Cambrian rocks of the 

 North- West Highlands. The G-eological Survey has divided this calcareous 

 sequence into seven well-marked groups, some of which have as yet 

 yielded no fossils beyond worm casts. Attention will presently bo 



1 Smithsonian Misc. Coll., vol. Ivii, No. 3, 1911. 



2 Geol. Mag., 1883, p. 126. 



