Geology and Mineralogy. 69 



out and in each case a typal qualifier derived from a geographic 

 root has been applied to the magmatic name of the new system, 

 to indicate the modal appearance presented by the minerals, tex- 

 ture, etc. The author has also cast the petrographic description 

 into a certain definite form which is proposed for future usage. 

 The work may thus be taken as a practical example of the new 

 system ; the many new names and terms and the definiteness and 

 conciseness of the descriptions will make it appear very strange 

 to those accustomed only to the more or less general names and 

 indefinite methods of description prevailing under the old ter- 

 minology and classifications. For the benefit of such the older 

 names, as well as the newer ones, are used to designate the rocks. 



It is especially on the chemical side that this work exhibits its 

 highest value ; a great number of analyses of the rocks of central 

 Italy have been previously made, but they are either old, so that 

 the analytical methods were inadequate to* yield complete and 

 accurate results, or they have been made by persons whose train- 

 ing and experience were not extensive enough to enable them to 

 obtain results sufficiently complete and exact to meet the de- 

 mands made by modern petrographical science. The rocks of 

 central Italy have been so long well known and many of them 

 have been so often studied in other ways that they have become 

 classic in the literature of petrography : the lack of thoroughly 

 complete and trustworthy analyses has been felt to be a serious 

 gap in our knowledge concerning them, and this contribution by 

 Washington is therefore particularly valuable and timely in sup- 

 plying this omission. The institution under whose patronage 

 this work has been carried on and finally brought out is to be 

 congratulated, no less than the author, on the excellence of the 

 results which have been obtained. . l. v. p. 



7. Geology and Petrography of Mt. Yamaska, -Province of 

 Quebec ; by G. A. Young. Ann. Rep. Geol. Surv. Canada, vol. 

 xvi, Pt. H, 43 pp. +map. — Through the investigations of Prof. 

 F. D. Adams and his associates the line of igneous intrusive 

 masses extending eastward from Montreal, and to which he has 

 given the name of the Monteregian Hills, have proved petro- 

 graphically of great interest. In this complete and careful study 

 of one of them by Dr. Young another chapter has been added 

 to our knowledge concerning them. 



The mountain consists of a volcanic neck of igneous rock 

 projecting upward through the Cambrian-Silurian sediments, 

 which have been considerably metamorphosed by it. Several 

 varieties of igneous rocks compose the mass, ranging from feld- 

 spathic to ferromagnesian types, and their arrangement and gra- 

 dations into one another are such as to lead to the belief that 

 they have been produced by differentiation in place, with some 

 subsequent movement. The types described consist of syenite 

 (var. akerite), essexite and a very basic variety termed yamaskite. 

 These are associated with, or cut by, dikes of syenite-aplite, nephe- 

 lite-syenite, bostonite and camptonite. The general arrangement 



