Revietvs — Aids in Practical Geology. 91 



The ore dej)osits are genetically connected with the igneous rocks 

 and occur in veins which are later than the dykes. The lodestuff 

 consists of brecciated material showing two periods of movement and 

 mineralization. The structure of the ores indicates that the earlier 

 mineralization led to the introduction of large amounts of chalco- 

 pyrite, with small quantities of gold and molybdenite. Part 

 of the chalcopyrite has replaced secondary actinolite, giving rise 

 to the name " hornblende ore ". The later minerals are zinc- 

 blende, tetrahedrite, argentiferous galena, chalcopyrite (in small 

 quantities), with banded quartz and some carbonates. 



The relation of the veins to the granodiorite appears to have a 

 direct bearing on the mineral paragenesis. Thus, those veins which 

 occur within the boundaries of the larger igneous masses are 

 characterized by the additional presence of magnetite and haematite, 

 and those near the contact by pyrrhotite and arsenopyrite. Magne- 

 tite is stated to have jDreceded the pyrrhotite, as it has been partly 

 replaced by it. Tourmaline also occurs, rarely. A point of interest 

 here brought out is the relation of the two groujDs of ores, indicating 

 a phase-sequence of mineralizations, separated by an interval of time, 

 during the last stages of consolidation of the igneous rock. The 

 report is illustrated by excellent microphotographs of polished 

 specimens of ores. 



Aids in Practical Geology. By Professor Grenville A. J. 

 Cole, F.R.S., M.R.I.A. Seventh edition, pp. xvi+431, 

 with coloured frontispiece, 2 plates, and 136 figures. London : 

 Charles Griffin & Co., Ltd. 1918. Price 105. U. 

 rpHIS book was first published nineteen years ago, and it is 

 -*- sufficient testimony to its usefulness that it has now reached 

 a seventh edition. The author has made few changes in the present 

 issue, which does not differ greatly from the third edition ; neverthe- 

 less, the work is well uj3-to-date, and such alterations as seemed 

 desirable have been carried out. It is not intended to take the place 

 of an ordinary textbook of geology, but rather to supply an aid to 

 the student working in the field, helping him to interpret what he 

 observes and to determine the character of the specimens he collects, 

 whether they be minerals, rocks, or fossils. It is impossible for 

 a field-geologist to carry his interest very far and to apply his 

 knowledge very closely without some acquaintance with the common 

 types of fossils and of their chronological and evolutionary 

 significance, and the author has done wisely to include an illustrated 

 account of the more important groups of fossil invertebrates. We 

 venture to hope that in a future edition, which should soon be 

 reached, he may add some description of the commoner vertebrate 

 remains, especially such as are found in this country. The work 

 is very appropriately dedicated to the memory of the late 

 Professor Judd. 



F. H. A. M. 



