Tin: I.OWKK SILUUIAN. 79 



Iviiifr the Wentworth series, but destitute of fossil remains. These, 

 with their continuation in the district extending eastward from the 

 Cobequidsto the Strait of Canso and into Cape Breton, were character- 

 ized l)y me in 1850* as consisting of " various sUitcs and quartzites, 

 with syenite, greenstone, compact felspar, claystone, and porphyry," 

 and were named in Acadian Geology the "Cobequid group," and their 

 age defined as intermediate between that of the lower Arisaig fossili- 

 ferous series and the Gold series (Cambrian) of the Atlantic coast. 

 As they had afforded no fossils, and as there seemed to be a litho- 

 logical and stratigraphical connection between them and the lower part 

 of the Upper Silurian, they were placed with that series as a dovvn- 

 ward extension, or, in part, metamorphosed members of it. 



The arrangement of these rocks in the central part of the Cobequids, 

 and also between the East River of Pictou and the east branch of 

 the St Mary's River, may be stated thus. There is a central mass of 

 red intrusive syenite or syenitic granite, usually having a large pre- 

 dominance of red orthoclase, with a moderate quantity of hornblende 

 and quartz. This sends veins into the overlying beds, and is itself 

 penetrated by dykes of diabase. On this central mass rests a great 

 thickness of felsites, porphyries, felsitic agglomerates, and diorites, 

 evidently of volcanic origin. Upon these are gi'ay, black, and red- 

 dish slates and quartzites, with a bed of limestone, and penetrated 

 by metallic veins. The lower volcanic portions and the upper more 

 strictly aqueous parts might perhaps be separated as a Lower and 

 Upper Cobequid series ; but the difference appears to depend rather 

 on mode of deposition than on any great difference of age. 



Along the northern side of the Cobequids, and between Pictou and 

 Arisaig, these beds are seen immediately to underlie the Upper 

 Silurian rocks, which have been disturbed with them, and are 

 penetrated by the same igneous dykes. Dr Honeyman appears to 

 have observed the same I'elation on the Lochaber Lake and in other 

 parts of Antigonish County. This somewhat constant association would 

 seem to uidicate that the rocks in question immediately underlie the 

 Upper Silurian, and are therefore themselves of Lower Silurian age. 

 On the other hand, their similarity in mineral character Avith the 

 lluronian scries of New Brunswick, with rocks observed in Cape 

 Breton to rise from under Cambrian deposits, and with the Huronian 

 rocks of Murray in Newfoundland, might induce us to assign them to 

 an earlier date. There are, however, some differences in mineral 

 character ; as, for example, the greater prevalence of olive, black, and 

 micaceous slates, and of highly felspathic rocks in the Cobequid series, 



''■' Journal of Geological Society, vol. vi. 



