October 24, 1901] 



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641 



manite, gneisses, biulitic granular, wilh two micas, scaly with 

 microcline, fine graiiied biotitic, nodular amphibolic, diorilic, 

 augito-hornblendic and fine-grained tormaliniferous ; augitic 

 granuliles, amphibolites, olivine and serpentiniferous rock and 

 calciphyres {i.e. crystalline calcific rocks containing more or less 

 various silicates). In the appendix is included an examination 

 of the granitites of Roccapietra, ()uarna, and some vein 

 granites. 



The second group comprises diorites — micaceous, augitic and 

 hornblendic ; norites — simple and with hornblende ; gabbros 

 — simple and with garnet and with olivine ; peridotites, jn'ro- 

 xenites and hornblendiles are represented by Iherzolites, harz- 

 burghites and websterites. The banded gabbros and stronalites 

 are represented by banded augitic gabbros, banded hornblendic 

 gabbros, stronalites. Basic dyke rocks, as spessartites, amphi- 

 bolites and dioritic schists, are each given their share of micro- 

 scopic researches. Some interesting observations are olTered 

 concerning the occurrence of schistose structure in these rocks. 



Under group three are included light-coloured schistose 

 gneisses, mica-tchists and prasinitic rocks. A notable fact in 

 this formation is the presence of thick bands and big masses of 

 truly mas-jive granitoid rocks intercalated between the more 

 schistose kinds. These are of different types in which the 

 characteristic element may be microcline, quartz, or of the type 



even in outline a review of this in the space at our disposal. A 

 clearer idea of the varied rock-struclures is afforded by the large 

 number of admirable photo-micrographs which the authors have 

 executed themselves, and which are extremely well reproduced 

 in the twenty plates devoted to this part of the subject. 



The second section of the memoir is devoted to the geological 

 characters of the rocks. Unfortunately, the authors are able to 

 add little that is new, or add any facts of general inteiest. 

 Observations of dip are recorded, as well as contact-phenomena 

 between rocks of divers mineralogical and chemical composition. 

 These physico-chemical effects seem to be most variable — highly 

 developed at one spot, and hardly to be remarked at others ; no 

 attempt, however, is made to explain the.se variations. 



The authors deny the absence of contact effects, as asserted 

 by Schaefer and Salomon, and between the basic eruptive rocks 

 and the gneiss of Strona, and give some striking examples. 

 As to ihe basic eruptive rocks, the authors show they are 

 posterior to the Strona gneiss, and discuss their relative age to 

 the Sesia gneis.s. The other groups are treated rather from the 

 point of view of their petrographical characters than from their 

 geological aspect. \^r ' "'J 



Cleavage and foliation, the effects of dynamo-metamorphic 

 processes, is well developed in one part of the region, and 

 quite absent in another ; but few details of the types of foliation,. 



of an augite-horneblende diorite. Though not attaining any 

 notable development, still the nodular or y^i/ gneisse.s are inter- 

 stratified with the other rocks of this formation, especially at Valle 

 de Carcoforo and other localities. 



Another member of this group which owes its structure to 

 dynamic metamorphism is the finely-banded gneisses in the Val 

 Grande. The structure of the limestones, calciphyres and schists 

 of Rimella and Forbello are each carefully described. 



The fourth group, included under the name of greenstones 

 (pietre verde), though of less importance from the point of view 

 of mass, present undoubtedly the most varied characters, such as 

 prasinites, amphibolites, amphibolic schists, eclogites, serpen- 

 tine, and oliviniferous rocks, calc-schists and saccharoidal lime- 

 stones, garnetiferous mica-schists, and light-coloured gneisses 

 and quartzite schists. 



The final or fifth group, or gneisses of Monte Rosa, are remark- 

 able for their uniformity of composition. The variations seem 

 to consist chiefly of a porphyroidal, schistose, banded or tubular 

 structure, passing by gradations to microgneisses and mica-schists. 



The petrographical description of this large number of divers 

 rocks and their varieties is very detailed, and appears to be 

 done with much care. It is, of course, quite impossible to give 



NO. 1669, VOL. 64] 



and other changes, are offered the reader. The difference o 

 interpretation of the relative ages and relations of the Strona and 

 Sesia gneisses, with Parona, is fully portrayed in a tabular form 

 of Messrs. Artini and Melzi's views. 



The greenstones of this region the authors collegate, and 

 even consider to be identical, wilh the greenstones of the Western 

 Alps, lately pronounced by the Coiiiilalo Geologico to be Triassic 

 and Liassic ; whilst the gneiss of Monte Rosa they consider as 

 Palaeozoic or even Archaic. 



A good geological map in colours of the region under con- 

 sideration is given, and another coloured plate is devoted to 

 sections. This work represents a great deal of patient labour 

 in a difficult region, and, altogether, the authors are to be con- 

 gratulated on their work. A little more charity to their oppo- 

 nents might here and there be allowed. It might also suggest 

 itself to their mind that Germany does not hold a monopoly of 

 petrographical research ; that in France, and even in poor little 

 England — not to speak of America, Norway, and other coun-. 

 tries— many problems that are concerned in this memoir have 

 been tackled, the published results of which might afford them 

 some additional information. 



II. J. Johnston-Lavis. 



