C URRENT PRE- CA MBRIA N LITER A TURE 439 



and this may be true of all. The gabbro breaks through both gneisses 

 and limestones. It presents two phases, an anorthosite, and a gabbro 

 containing abundant pyroxene and other ferro-magnesian minerals. In 

 places also in the western Adirondack^ the granites and syenites break 

 through the limestone. 



Barlow 1 gives a further account of the results of work being carried 

 on by himself and Dr. Adams in the counties of Hastings, Halibur- 

 ton, and Renfrew, Province of Ontario. Many of the so-called 

 conglomerates of the Hastings and Grenville series are believed to be 

 autoclastic rocks or pseudoconglomerates which have resulted in the 

 main from complex folding and stretching. Therefore such rocks 

 cannot be cited as evidence of the clastic origin of the Hastings and 

 Grenville series, as has been done. 



Barlow 2 describes the geology of the Nipissing-Temiscaming map- 

 sheets, comprising portions of the district of Nipissing, Ontario, and 

 the county of Pontiac, Quebec. 



Laurentian and Huronian rocks occupy most of the area. These do 

 not include a few small isolated inliers of crystalline limestone and 

 gneissic rocks which resemble the Grenville rocks to the south and 

 southwest. These are so small in quantity that they are not mapped. 

 Their relations to the Huronian are not discussed. 



The Laurentian rocks occupy the two thirds of the area of the two 

 sheets. While probably representing in part the first formed crust of 

 the earth, and therefore the basement upon which the Huronian rocks 

 were laid down, the Laurentian has undergone successive fusions and 

 recementations before reaching its present condition. It is now a 

 complex of plutonic rocks which in general show irruptive relations to 

 the overlying Huronian series. However, on Lake Temiscaming the 

 Laurentian is unconformably below, and in direct contact with, an 

 arkose of Huronian age, which has apparently been derived from the 

 disintegration the Laurentian granite. 



The Huronian occupies about a third of the combined area of the 

 two sheets. It is separable into three divisions, in ascending order as 



1 On the Origin of some Archean Conglomerates, by A. E. Barlow : The 

 •Ottawa Naturalist, Vol. XII, 1899, pp. ,205-217. See Am. Journ. Sci., 4th series, Vol. 

 Ill, 1897, pp. 173-180. 



2 Geology and Natural Resources of the Area included by the Nipissing- 

 Temiscaming Map-sheets, comprising Portions of the District of Nipissing, Ontario, 

 and of the County of Pontiac, Quebec, by A. E. Barlow : Ann. Report Geol. Surv. 

 •of Canada, Vol. X, Pt. 1, 1899, PP- 302- With geological map. 



