REVIEWS 727 



name Huronian has been applied to quite different series; by using these 

 local names for the Temiskaming region one avoids confusion. 



The Bruce series consists of quartzites, conglomerates, limestones, 

 and greywackes. The Cobalt series contains quartzites, conglomerates, 

 both basal and slaty, and cherty limestone. As at Cobalt, so at Bruce 

 the Cobalt slate conglomerate carries striated bowlders. 



T. T. Q. 



Uber die Parallelstruktur des Gletschereises . By Axel Hamberg. 

 ge Cong. Internat. d. Geog., 1908, Compte rendu II. Pp. 7, 

 pis. 4. 



In general two sorts of parallel structure are to be observed in glaciers, 



that due to the original snow bedding in the collecting area, and that of 



secondary origin which is vertical and parallel to the longitudinal axis 



of the glacier. By some it has been thought that the vertical parallel 



structure was only the original horizontal snow bedding turned up on 



edge through pressure. It is desirable to know whether "regenerated" 



glaciers show the vertical parallel structure and how it is formed. The 



author after a study of a number of glaciers in Sweden and Spitzbergen 



concludes that the structure in question has relation to the movement of 



the ice. When there is a downward slope in an ice sheet, the very great 



downward pressure of the ice from gravity has a forward component 



which tends to cause movement along the valley. Friction of the sides 



and bottom of the valley retards the motion of ice layers next to them, 



so that the ice is broken into parallel bands which move forward at 



differential rates, the upper central bands moving the more rapidly. 



The planes of differential motion are influenced by every irregularity of 



the containing valley and may be trough-shaped. 



R. C. M. 



The Grain of Igneous Rocks. By A. C. Lane. Ann. Rept., Board 

 Geol. and Biol. Surv., Michigan (191 1), pp. I45-7 1 - Fig s - 5- 

 The grain of an igneous rock depends on a number of factors, among 

 which may be noted the chemical and mineralogical composition of the 

 rock, its retention of solvent gases and mineralizers, pressure, and rate 

 of cooling. The last named is one of the most important, and it is 

 observed that there is a direct ratio between the size of the grain and 

 distance from the cooling surface, the effect being most advantageously 

 studied in the mineral grains which are last to crystallize. With due 



