Rei-ieics — Mficnair's Geology of the Grampians. 33 



chapter expounds some of the principles of geology, and is apparently 

 intended for the novice. The following Historical Introduction 

 plunges into technicalities at once, and is stiff reading for the novice 

 ■who has only the first chapter to guide him. It consists mainly of an 

 exposition of Nicol's work on the structure of the Southern Grampians 

 and a summary of the author's views as developed in the succeeding 

 chapters. 



In chapter iii, which gives an outline of the physiography and 

 geology, the former subject is largely taken up by lists of mountain 

 summits, tributary streams, and the names of hills seen from certain 

 view points, from which the reader is likely to emerge with the 

 haziest of notions about the physiography of the region. The outline 

 of the geology is a more useful summary, though such phrases as the 

 "summit of the synclinal trough" are puzzling, and we note the 

 remarkable statement that "the presence of roches inoutonnees indicates 

 the existence and work of the later glaciers". 



Chapters iv and v contain a description of the rocks of the Highland 

 area. They are classified into schists of sedimentary origin, schists of 

 igneous origin, and intrusive rocks later than the foliation of the 

 schists. The author points out that the bulk of the rocks were laid 

 down as sediments of the ordinary type, and that many of them retain 

 traces of their original fragmental character. The weak and fine- 

 grained sediments are more affected by metamorphism than the harder 

 rocks, but, apart from the original nature of the sediments, the 

 metamorphism which is feeble in certain areas increases in intensity 

 in others, often at no great distance. The author considers the 

 metamorphism to be mainly dynamic, the rocks having been subjected 

 to great pressure, accompanied by a high temperature, during the 

 operation of the mountain-building processes which upheaved the 

 Grampians. He does not distinguish any effects particularly due to 

 thermal metamorphism, and whilst admitting "high degrees of heat" 

 lie offers no opinion as to its source. In areas of feeble metamorphism, 

 such as the belt of slates on the margin of the Highlands, one set of 

 cleavage planes only is recognized, but in the zone of the Ben Lawers 

 schist the first, cleavage planes are folded and crossed by a second set 

 of cleavage planes developed during the folding of the first set. In 

 some districts tertiary and even quaternary cleavages may be traced, 

 and these, the author thinks, were produced by a series of intermittent 

 movements. The author does not appear to distinguish cleavage from 

 foliation, and slaty cleavage is not separated from the false cleavages. 

 One of the latter structures, strain-slip-cleavage, is referred to as 

 ' strain-slip', but if the full title be considered too unwieldy, 'slip- 

 cleavage' would be a more suitable abbreviation. The mineral 

 changes which accompany the development of foliation are scarcely 

 mentioned. 



It is well known that the schists which enter into the formation of 

 the Grampians traverse that region in a north-west and south-east 

 direction. These the author divides into the following zones, omitting 

 a narrow baud of black slates, cherts, and limestones, the supposed 

 Arenig rocks of the Survey on the Highland frontier, and the Leny 

 grits for consideration in a later chapter: (1) The Lower Argillaceous 



DECADE V. — VOL. VI. — NO. I. 3 



