CURRENT PRE-CAMBRIAN LITERA TURE 423 



Comments.— In. the explorations by Tyrrell and Low, considering 

 the time available and the ground covered, the determination of the 

 geological series was necessarily of the most hasty nature. Nothing 

 but the roughest petrographical discriminations could be made, and no 

 structural work was possible. Their terms Laurentian, Huronian, and 

 even Cambrian, therefore, indicate only the broad petrographical 

 features of the rocks traversed, and do not stand for well defined 

 series equivalent to the series so named to the south. 



Following the usage of many of the Canadian geologists, the 

 Cambrian is made to include rocks supposedly equivalent to the 

 Cambrian, Keweenawan, and Animikie of the Lake Superior region, 

 and Low carries it down even to include formations similar to Lower 

 Marquette formations of the Lake Superior country. In the Lake 

 Superior region, where most thoroughly studied, the Keweenawan and 

 Huronian formations are separated from each other and from the 

 Cambrian by well marked unconformities, unconformities uniformly 

 recognized by geologists who have done close work in this region. 

 These unconformities have been recognized also in other parts of North 

 America. If the rocks above called Cambrian are really equivalent to 

 the various Lake Superior series mentioned, then the extension down- 

 ward of the Cambrian, across well established unconformities, to include 

 such series, has no reasonable basis. However, in view of the scanty 

 observations and the absence of connecting structural work, any cor- 

 relation at present is little more than a suggestion, and for this reason 

 it would be better to give the formations local names, as was done by 

 Tyrrell in the case of the Athabasca sandstone. Thus would be 

 avoided the confusion arising from the misuse of well defined and well 

 established terms like Cambrian, Keweenawan, and Huronian. 



Bailey 1 reports on the geology of southwest Nova Scotia. Cambrian 

 rocks devoid of fossils occupy a large part of the area. The succession 

 is, in ascending order, as follows: 



I. Quartzite Division. 



(a) Heavily bedded bluish quartzites, alternating with much thinner 

 beds of argillite. 



(b) Greenish-gray sandstones or quartzites, somewhat chloritic and 

 less massive than in (a), and alternating with slates which are 

 arenaceous below but become progressively more argillaceous 

 above. 



'Report on the geology of southwest Nova Scotia, by L.W.Bailey: Ann. 

 Rep. Geol. Surv. of Canada, Vol. IX, 1898, part M, p. 154. With geol. map. 



