382 Proceedings of the Boyal Physical Society. 



Billings to underlie rocks which, at Cow Head and other 

 places, yield such typical Lower Arenig Graptolites as 

 Phyllograptus, Tetragraptus, Bryograptus, and Callograptus} 

 It is inferred, therefore, that the underlying rocks represent 

 the top of the Cambrian formation. It follows, therefore, 

 that these zones of the Durness Limestone are probably 

 Upper Cambrian; and in further confirmation of this in- 

 ference, Messrs Macconochie and Tait last year found, both 

 in Skye and Durness, some trilobite remains of a Middle 

 and Upper Cambrian facies.^ 



It may now be considered that the Durness Limestone 

 probably represents the Middle and Upper Cambrian, and 

 perhaps also the base of the Lower Silurian or Ordovician 

 formations. The Lower Cambrian appears to extend 

 upwards into the first thirty feet of the Durness Limestone, 

 which contains two thin zones crowded with Salter ella rugosa 

 and >S^. pulchella, fossils of the Olenellus zone.^ It embraces 

 the Serpulite grit and Fucoid beds, and extends downwards 

 to at least as far as the third subzone of the Upper Quart- 

 zite, or " Pipe-rock," Mr Cadell having recorded the occur- 

 rence of Salterella Maccullochii from that horizon.^ The 

 underlying zones of the Quartzite, down to the unconform- 

 able base-line, having afforded no fossil evidence beyond 

 that of the vertical cylinders of sand ('' pipes "), the Scolithus 

 linearis of American palaeontologists may even be pre- 

 Cambrian in age ; but it has been found convenient to retain 

 them in the Cambrian formation till evidence to the con- 

 trary is forthcoming. 



Although Professor Lapworth's paper on the "Moffat 

 Series " ^ had already laid the basis for the classification of 

 the Silurian rocks entering into the Southern Uplands of 

 Scotland, yet, during the period under consideration, a good 

 deal of work has been done in that direction : thus Professor 

 Lapworth's discovery of Phyllograiotits, Tetragraptus, and 



1 Oeol. Sur. Canada, "Palreozoic Fossils," Billings, vol. i. pp. 336-376, 

 1861-65. 



2 Mem. Oeol. Sur., "Report of Progress for 1899," p. 186, 1900. 



=^ Quart. Jour. Geol. Soc, vol. xliv. p. 408, 1888. * Ibid. 



5 Quart. Jour. Geol. Soc, vol. xxxiv. pp. 240-346, 1878. 



