642 REPORT — 1901. 



MONDAY, SEPTEMBER 16. 

 The following Papers and Keports were read: — 



1. The Cambrian Fossils of the North-west Highlands. 

 By B. N. Peach, F.R.S. 



[Communicated by permission of the Director of the Geological Survey.] 



The Cambrian roeks of the north-west of Scotland occur within a narrow 

 belt of countr_y, less than ten miles wide, stretching from Durness and Eireboll to 

 Skye, a distance of 120 miles. 



The lowest member consists of quartzite 500 feet thick, the under half of 

 which is false bedded and devoid of organic remains, and the upper part of which 

 is finer grained and more evenly bedded and pierced by worm pipes, ' Scolithus 

 linearis,' by means of different forms of which it can be divided up into five 

 sub-zones. The succeeding ' fucold beds,' consisting of fifty to eighty feet of green 

 niudstone.?, dolomites, &c., have yielded three species of Olenellus, nearly allied to 

 Olenellus T/winsoni. The serpulite grit, from ten to thirty feet thick, usually 

 crowded with Salterellas, has also yielded a species of Olenellus. It is overlaid 

 by a vast column of dolomite, limestone, and subsidiary beds of chert, amounting 

 in all to 1,200 or 1,500 feet in thickness. The first tliirty feet of the limestone 

 has yielded two species of Saltcrella, and the beds up to that point are looked 

 upon as the equivalents of the Olenellus or Georgian Terrane of North America, 

 the whole facies of the fauna being exceedingly lilie that of America. 



The overlying column of dolomite, &c.. Las been divided into seven sub- 

 zones, varying in thicltness from 100 to 400 feet, the three uppermost zones of which 

 have yielded a fauna almost identical with that described by Billings and others 

 from rocks wliich in Newfoundland and the St. Lawrence region of Canada 

 underlie black shales at Cow Head and Point Levis, yielding a long suite of 

 graptolites characteristic of the Phyllograptus or Arenig zone. The Durness 

 dolomite must therefore represent the Middle and Upper Cambrian horizons, and 

 perhaps the base of tlie Ai-enig of America and Europe. 



As regards the conditions under which these deposits were laid down, the 

 author considers that the basal quartzites show proximity to a low shelving shore 

 line continuous across what is now the Atlantic to America, more or less 

 parallel to the shores of what is now Western Scotland, and a little to the north 

 of the present area ; that owing to more or less continuous depression of the area, 

 the ' pipe roclc ' was deported further from shore, the ' fucoid beds ' representing 

 the period when the ' mud line ' or limit of sedimentation was reached, while 

 the vast pile of the Durness dolomite represents tlie debris of the ' I'lankton ' 

 that fell en the bottom of a clear though not necessarily a deep ocean. Solution 

 of great part of the calcareous ooze while exposed to tlie action of sea water, 

 and perhaps substitution of magnesian salts for calcareous ones, changed the 

 calcareous oozes into dolomites, while the chert beds represent the reasserted 

 remains of the silicious organisms. 



The author pointed out that in Arenig times the sea over what is now the 

 northern part of the southern uplands of Scotland was also a clear one, free from 

 terrigenous sediments, and in which a radiolarian deposit accumulated. If the 

 rocks along the Highland border described by Messrs. Darrow, Clough, and 

 Gunn be the northern continuation of these southern upland rocks, then it is 

 rendered highly probable that in late Cambrian and early Silurian times a clear 

 sea lay across what are now the Highlands of Scotland, which was probably the 

 barrier which divided the Cambrian faunas of America and North-west Scotland 

 on the one side from those of Wales, Bohemia, and the Baltic region of Europe 

 on the other. 



