84 Reviews — Dr. E. W. Skeats — Heathcote Rocks, Victoria. 



for himself drawings of crystals in clinographic projection, sucli as he 

 sees — but does not always understand — in textbooks of mineralogy. 

 The author uses graphical methods to solve the problems that arise 

 in the pictorial representation of crystals, some of which are very 

 ingenious and cannot fail to appeal to those numerous students who 

 are not blessed with the mathematical faculty. In each system the 

 mode of drawing the areas, in the conventional positions adopted by 

 crystallographers, is first described, and then the methods of drawing 

 around these the various simple forms either alone or in combination. 

 The book is well illustrated by original drawings made by the author 

 herself, and the text is written in a simple, clear, and refreshingly 

 unacademic style. Anyone to whom the subject is new, who desires 

 to obtain a clear idea of the geometrical side of crj'stallography, will 

 find Miss Eeeks's book most helpful. 



C. G. C. 



VI. — On the Evidence of the Origin, Age, and Alteration of the 

 EocKS NEAR Heathcote, Yictoria. By Ernest W. Skeats, D.Sc, 

 A.R.C.S., E.G.S. Proc. Ptoy. Soc. Yictoria, vol. xxi (new series), 

 pt. i, August, 1908. 



nj^HE area in question lies about 75 miles north of Melbourne. It 

 \_ consists of Silurian and Ordovician sediments, the former to the 

 east, the latter to the west. (A part has even been regarded as 

 Cambrian, by Etheridge.) Between these two areas of unaltered 

 sedimentary rocks there occurs a zone of igneous rocks and associated 

 "cherts and jasperoids ", forming a linear outcrop some half a mile 

 in width running roughly north and south across the district. The 

 igneous materials are mainly diabases and diorites, but " microgranites, 

 granophyres, and felspar porphyrites " also occur, especially in the 

 immediate neighbourhood of Heathcote. The exact age of these 

 igneous rocks and their relation to the adjacent sediments, and the 

 true nature and mode of origin of the cherts and jasperoids, are 

 controversial questions of long standing in Victorian geology. 

 Professor Skeats's paper is a notable addition to those already con- 

 tributed on the subject by Dunn, Lidgey, Howitt, Gregory, etc. 



By some the diabases have been regarded as of intrusive, by others 

 as of effusive origin, by some as of pre-Silurian, by others as of 

 post-Silurian or even pre-Ordovician age. Professor Skeats gives his 

 reasons for considering them to be effusive rocks of Lower Ordovician 

 age. The paper, besides recording the results of the author's own 

 field and laboratory work, includes also a review and discussion of 

 the previous literature on the district. The following extract best 

 expresses the author's vicAvs : — 



"With regard to the conclusions at which I have arrived in this 

 paper, I find myself only in partial agreement with previous workers. 



" I am in agreement with Mr. Dunn in regarding the diabases as 

 mainly effusive. With Professor Gregorj^ I agree that the diabase 

 is pre-Silurian, and with Dr. Howitt that the Ordovicians are altered 

 along the contact with the diabase, and that the black cherts are 

 altered Ordovician rocks. On the other hand, I disagree with 



