Reviews — Dr. A. C. Laicson — The Rainy Lake Region. 37 



the mica-schists principally in containing felspar. The structure of 

 both rocks is the same. The original rocks are supposed by the 

 author to have been of sedimentary origin. 



The Keewatin series is much more variable in character. It 

 includes diabases, hornblende-schists, soft fissile green schists, 

 conglomerates, sericite schists, felsitic schists (altered quartz- 

 porphyries) greywackes and volcanic tuffs. 



The "bedded traps or greenstones" give the character to this 

 series. They have suffered more or less alteration (a) by meta- 

 somatic processes, (6) by dynamic action. Those which have been 

 affected by the first set of processes only preserve the original 

 structure so as to leave no doubt as to the original characters of the 

 rocks. Some have the ophitic structure of diabases, others the 

 granular structure of gabbros. Those which have suffered dynamic 

 metamorphism have lost their original structure to a greater or less 

 extent, and taken on that of a schistose or foliated rock. The 

 constituents of these more or less altered basic igneous rocks are 

 felspar, pyroxene, fibrous and compact hornblende, titaniferous 

 iron ore, apatite, leucoxene, zoisite, epidote, chlorite, calcite, and 

 quartz. The rocks are described by the author under such names 

 as uralitic and saussuritic gabbro, uralitic diabase and porphyritic 

 diabase. It is evident from the detailed descriptions with which the 

 Memoir abounds that the rocks are similar to varieties of greenstone 

 occurring in the West of England. 



The hornblende-schists are regarded by the author as being in 

 part altered massive rocks, and in part altered pyroclastic rocks of 

 basic composition. The felspathic varieties approach diorites in 

 structure and composition. Dynamic action has certainly deter- 

 mined the structure of these rocks, but it has operated before the 

 final stages of recrystallization were complete, for the individual 

 constituents do not show any of those effects of pressure which are 

 so common in the schistose diabases. 



The soft green fissile schists are usually bedded and are probably 

 metamorphosed pyroclastic rocks. 



The matrix of the conglomerates is a dark green chloritic or 

 hornblendic schist. The pebbles are often well-rounded and reach 

 as much as a foot in diameter. They consist of saccharoidal quartz, 

 felsite, quartz-porphyry and granite. It will be noted that pebbles 

 of Laurentian gneiss are conspicuous by their absence. 



The sericitic and felsitic schists are merely altered quartz- 

 porphyries. They are associated with acid volcanic tuffs and 

 agglomerates. 



In addition to the volcanic rocks which form the bulk of the 

 sei'ies there are grits or greywackes, which consist, for the most 

 part, of ordinary sedimentary material. 



Owing to the enormous jamming together which the rocks have 

 undergone it is not possible to estimate the thickness of the Keewatin 

 series. It must, however, have amounted to many thousands of feet. 

 Their general disposition is that of a sharply folded trough, sinking 

 down into the gneiss which flanks it on either side. The horn- 



