THE CAMBRIAN SYSTEM 97 



are Gastropoda, but bivalves (Lamellibraiichia and Brachiopoda) 

 are not rare. Archceocyathus (see p. 72) is of frequent occurn-n. , 

 as are also sponges of the genus Calathium or Archteotcyphia. 



In 1891 fragments of Olenellus (0. Lapworthi) and specimens of 

 llijnlithes were found in the Serpulite grits and Fucoid Bed* of 

 Ross, proving them to be of Lower Cambrian age. Hence it i 

 probable that the lower part of the Calcareous Series is of Mi<lUf 

 Cambrian age (Paradoxidian), but the higher and more fossiliferous 

 part is of Upper Cambrian age, corresponding to the Upper Lingula 

 flags and Tremadoc slates of Wales. 



The Cambrian succession in Skye has been worked out by Mr. 

 C. T. Clough, who found that the same subdivision could be made 

 as in Durness. Moreover, the Olenellus fauna was again discovered 

 in the Fucoid Beds at Tokavaig and Ord. No fossils, however, 

 could be found in the lower part of the Durness limestone, the 

 thickness of which to the top of the Sailmhor Group Mr. Clough 

 estimates at 830 feet. But higher beds are found in Strath, and 

 in 1898 these yielded many fossils, including Calathium and 

 Archceoscyphia a trilobite of the genus Solenopleura ; Orthirina 

 festinata and 0. striatula ; a bivalve, Euchasma Blumenbachite ; 

 species of Pleurotomaria, Murchisonia, Maclurea, and Holopea, with 

 Piloceras, Orthoceras, and Trecholites. 



The fauna of the Durness limestone, as regards both genera and 

 species, has much more affinity with that of the Cambrian of 

 North America than with that of Wales or England. It may in 

 fact be inferred that the Scotch Cambrian belongs to a North 

 Atlantic or North American area of life and deposition, in which 

 the physical conditions differed considerably from those of the 

 South British and Central European area. 



The only other part of Scotland where rocks occur which seem 

 to be of Cambrian age is along the south-eastern border of the 

 Central Highlands in Perth, Forfar, and Kincardine. They occur 

 in narrow faulted strips along a line from Blairgowrie in Perth to 

 Stonehaven on the coast, and consist of grey shales and grits, jasper 

 and jaspery phyllite, with lenticular sills and possibly interbedded 

 flows of basic igneous rock (dolerite). They were described by Mr. 

 G. Barrow as the " Green Rock and Jasper Series," '^ and from 

 the resemblance between them and rocks of Arenig age MI the 

 Southern Uplands he regarded them as probably Ordovician ; but 

 a more recent discovery of fossils in the same series as exposed on 

 the coast near Stonehaven makes it probable that they are of 

 Cambrian age. 



This discovery was made by Mr. R. Campbell K in a set of black 

 shales with layers of jasper and chert intercalated with bauds or sills 



H 



