484 



NATURE 



[Afarc/i 24, 1887 



and chemical composition, into a i^ranitic, a iyeiiitic, and 

 a dioritic series. 



Looking at the joclis, however, from the point of view 

 of habit and structure, ' three types, independent of 

 mineralogical composition, may be established, namely: 

 a "granitic" onl}- known to occur among the more acid 

 representatives ; a ^^ granito-porphyritic" which is repre- 

 sented in each of the above series ; and a '' lampro- 

 phyric" which appears to be unrepresented in the more 

 acid subdivisions. The following classification is accord- 

 ingly proposed for the " dyke-rocks " : — 

 (rt) Granitic dyke-rocks (aplite, tourmaline-granite, &c.). 

 {b) Granito-porphyritic dyke-rocks (granite-porphyry, 

 syenite-porphyry, eteolite-porphyry, diorite-porphyrite). 

 (t) Lamprophyric dyke-rocks. 



This last family may perhaps be best designated 

 as a refuge for certain classes of rocks, such as the 

 kersantites and kersantons, the minettes, and the 

 lamprophyres, which have been long wandering about 

 in the various systems of classification without finding 

 any fixed abode. It is further subdivided into the 

 syenitic lamprophyres (minettes and vogesites) and the 

 dioritic lamprophyres (kersantite and camptonite). 



Passing on to the group of the true Volcanic rocks, we 

 note an important distinction between them and those of 

 the Plutonic group, contained in a general law laid down 

 by the author in this chapter. A volcanic (effusive) rock 

 is always more acid and specifically lighter than its 

 plutonic equivalent. To explain this the author suggests 

 that an eruptive magma, during its slow ascent along 

 cracks in the earth's crust, differentiates according to 

 specific gravity, the heavier part, which ultimately gives 

 rise to the plutonic rocks that consolidate within the 

 earth's crust, being more basic, poorer in alkalies, and 

 richer in alkaline earths and iron, than the specifically 

 lighter part which reaches the earth's surface. 



The author then proceeds to discuss the recurrence of 

 phase in the crystallisation of the effusive rocks, and 

 defines porphyritic structure as that structure which is 

 produced by the recurrence of the same or similar 

 minerals at two distinct periods of crystallisation. It is 

 this structure which is the most essential characteristic of 

 the effusive rocks. It may, however, be developed in 

 very different ways. When the ground-mass is holo- 

 crystalline,the structure is " holocrystalline-porphyritic " ; 

 it is " vitro-porphyritic " when the ground-mass is glassy, 

 and " hypocrystalline-porphyritic " when the ground-mass 

 consists partly of vitreous, partly of crystalline elements. 



Of the Volcanic group only the pateovolcanic series is 

 discussed in the present volume. It is subdivided as 

 follows : — 



{a) Family of the quartz porphyries (palaeovolcanic 

 equivalents of the granites). 



(b) Family of the quartzless porph yries (equivalents of 

 the syenites). 



(c) Family of the porphyrites (equivalents of the 

 diorites). 



(d) Family of the augite-porphyrites and melaphyres 

 equivalents of the gabbros and diabases). 



{e) Family of the picrite-porphyrites (equivalents of the 

 peridotites). 



The neovolcanic rocks (rhyolites, trachytes, andesites, 

 basalts, phonolites, tephrites, &c.) are .reserved for the 



Second Part, which is promised for Easter of this year, 

 and will contain the plates to the whole volume. Thus 

 completed, the work will form a most valuable addition 

 to petrographical literature. One of its important fea- 

 tures is the full collation of literature under each head. 

 Students of petrographical science will thank Prof 

 Rosenbusch for the inestimable boon he has conferred 

 upon them in indexing almost all the papers dealing with 

 petrographical subjects which had appeared -up to the 

 date of publication of his book. 



Frederick H. Hatch 



LOCH CRERAN 

 Loch Cnran : Notes from the Western Highlands. By 



W. Anderson Smith. (Paisley and London ; Alexander 



Gardner, 1887.) 

 'npHE amateur naturalist who has leisure, a genuine 

 interest in his subject, and abundant opportunities 

 of exercising his observation, ought to be an exception- 

 ally happy person ; but he is not always well-advised in 

 rushing into print with the result of his fugitive studies. 

 That, however, is one of the foibles of the hour. The 

 public are supposed to welcome somewhat bald cata- 

 logues of the common objects of the way-side, the heath, 

 and the sea-shore ; the newspaper reporter is glad to be 

 temporarily withdrawn from the Divorce Court and sent 

 to describe the chestnut-trees in Bushey Park ; and 

 young ladies, who have got the length of distinguishing 

 between Ranunculus Ficaria and R. acris narrate in the 

 evening papers the story of their exploration of the hedge- 

 rows. The result is harmless enough. It is not science ; 

 it is not literature ; but it serves to teach a few people 

 here and there to keep their eyes open ; and that is 

 something. And perhaps a world groaning under a load 

 of books need not mind an additional volume or two — 

 which it is not compelled to read. 



Mr. W. Anderson Smith does not inform us whether 

 these " Notes from the Western Highlands " have been, 

 like some other of his writings, reprinted from a pro- 

 vincial journal ; but if they are so, he has done himself 

 injustice in not stating the fact ; for carelessness that is 

 comparatively venial in the columns of a newspaper 

 becomes vexatious in a book. And truth compels us to 

 say that Mr. Smith's style is slovenly in the extreme. 

 Mis-spellings abound : the few scraps of French or Latin 

 quoted are almost invariably mangled ; there is an occa- 

 sional lapse of grammar ; and now and again the heedless 

 composition provokes a smile, as when he says, " Into 

 the luxurious beds we sink up to the knees, many of them 

 at present with dainty seed-vessels ripe and full." And 

 yet there is a chatty simplicity here and there in the book 

 that is not without attraction. The ways and humours 

 of certain domestic pets are described in a kindly fashion 

 which recommends itself ; and there are incidental 

 glimpses of winter life and winter occupations in the 

 West Highlands that are sufficiently pleasant. As for the 

 bulk of the volume, that is devoted to marine zoology ; 

 and marine zoology, to be made interesting, not to say 

 intelligible, to the general reader, should be accompanied 

 by illustrations ; while, on the other hand, the trained 

 scientific student is not likely to concern himself much 

 with the unmethodical investigations here noted down. 



