270 



rocks of this group are all igneous and have generally 

 been considered to belong to the Pre-Cambrian. The 

 correlation of the strata in the Boisdale Hills has been based, 

 (i) on supposedly similar stratigraphical relations and (2) 

 on similarity in appearance. 



The Etcheminian is described as essentially a sedimentary 

 formation divisible into a lower and upper division. The 

 lower division consists largely of red and grey slates and 

 sandstones with conglomerate beds. The upper division 

 is composed mainly of grey, fine and coarse, shales and 

 slates. Both divisions are fossiliferous and besides a 

 number of species of brachiopods and osteracods, Matthew 

 has listed a trilobite "apparently related to Asaphus" 

 (Holasaphus centropyge), a Paradoxoid trilobite and one of 

 the genus Solenopleura. 



The Acadian division consists chiefly of dark grey 

 slates. It is unfossiliferous in the Boisdale hills area. 

 The Johannian is composed mainly of grey slates, sand- 

 stones and quartzites and has produced some fossils, 

 among them, Paradoxides forchhammeri , and a number of 

 inarticulate brachiopods. The Bretonian division is 

 chiefly formed of dark grey and black slates; among the 

 few fossils that have been found are species of Asaphellus, a 

 typical 'Tremadoc' genus. On the Mira river, the Bre- 

 tonian is much more richly fossiliferous and contains 

 faunas, strictly comparable to the Scandinavian Upper 

 Cambrian and Lower Ordovician. 



Matthew gives [2, p. 52) the following estimate of the 

 thickness of the Cambrian as developed respectively in the 

 Boisdale Hills area and in the Mira River valley not many 

 miles to the east. 





Boisdale hills. 



Mira river. 



Bretonian 



Feet. 



500 

 1 ,200 

 200 

 500 

 300 



Feet. 



500 

 2,000 



Johannian 



Acadian 



800 



Etcheminian 



3,000 

 very thick. 



Coldbrookian 





