Reviews — Dr. A. C. Laicson — The Rainy Lake Region. 39 



junction ; in the interior it is concentric with reference to one or 

 more centres. 



The author has paid special attention to the phenomena of the 

 inclusions. These inclusions are found, not only near the mai'gins 

 of the Laurentian areas, but also in the central portions. They vary 

 in size from that of one's fist to that of a house and even larger. 

 Near the junction a definite connection between the inclusions and 

 the surrounding rocks may be traced. Thus, at the contact with 

 hornblende-schist, the inclusions consist of hornblende-schist, and 

 at the contact with the Coutchiching series they consist of rocks 

 derived from that series. 



The inclusions are sometimes angular and sharply separated from 

 the gneiss, at other times they are lenticular and blend more or less 

 gradually with the surrounding rock. The elongated inclusions are 

 arranged with their longer axes parallel to the general foliation. All 

 the facts go to show that the parallel arrangement of the inclusions 

 and the foliation of the gneiss are fluxion phenomena. Certain 

 banded gneisses are regarded by the author as due to a stretching of 

 an intimate mixture of inclusions with the gneissic magma. The 

 memoir is illustrated by photographs of portions of the gneiss which 

 are rich in inclusions, and one of these (plate vi.) bears a most 

 striking resemblance to Fig. 2, Plate XIV. 1 Geol. Mag. Dec. III. 

 Vol IV. 1887. 



In addition to the points above referred to, the Memoir contains 

 much interesting matter. Thus it treats of the relation between 

 topography and geological structure, the petrographical characters of 

 numerous intrusive granites, the distribution and character of certain 

 later basic dykes, and the glacial phenomena of the district. 



As regards the origin of the Laurentian rocks the author pro- 

 pounds the theory that they represent the fused floor on which the 

 Coutchiching and Keewatin rocks were deposited, and to a certain 

 extent also of fused portions of these rocks. He insists, however, 

 strongly on the point that whatever may have been the origin of 

 the magma, the minerals of which the Laurentian rocks are com- 

 posed, and the structures which these rocks possess, owe their 

 origin to causes operating after the formation and folding of the 

 rocks with which they are in contact. 



In speaking of the topography of the Laurentian areas he says 

 " it is remarkably flat and devoid of prominent elevations, although 

 the surface in detail is extremely uneven and hummocky or mam- 

 millated. It presents for the most part the glaciated surface of the 

 rocks either quite bare or covered only by forests and forest loam. 

 The plateau abounds in lakes, which lie in rocky basins." This 

 description will be thoroughly appreciated by all those who are 

 acquainted with the Archaaan topography of the N.W. of Scotland. 



J. J. H. T. 



1 This plate illustrates a paper by the reviewer " On the Origin of Certain 

 Banded Gneisses." 



