58 Canadian Record of Science. 



can be proved to have been derived from any of the ordinary 

 types by a process of alteration. Thus there would be Rhyolites 

 and Aporhyolites, Andesites and Apandesites, and so on. 



Another point in the classification adopted by Prof. Zirkel is 

 the retention of the old use of the terms Diabase and Gabbro, the 

 former being a rock composed of plagioclase and augite and the 

 latter one composed of plagioclase and diallage, the distinction 

 between the two being thus made to depend on the presence or 

 absence of a cleavage parallel to the orthopinacoid of the pyroxene. 

 This cleavage, which is often nothing more than a parting, is now 

 generally considered to be a most unsatisfactory basis of division, 

 not nearly so good as that afforded by the ophitic (diabase) and 

 granitoid structures displayed respectively by the two rocks — which 

 structures although occasionally found in different portions of the 

 same mass, certainly form a better and more distinct ground of 

 classification than a more or less distinct or indistinct orthopina- 

 coidal parting in a single constituent. 



Prof. Zirkel's book is an excellent one and represents an 

 enormous amount of careful work, and will take rank with the 

 works of Pj-of. Rosenbusch as one which must find a place in the 

 library of every petrographer. Frank D. Adams. 



Notes on the Geology of Middleton Island, Alaska, by 

 George M. Dawson, C.M.G., LLJ)., F.E.S., F.G S., 

 Bull. Geol. Soc. America, vol. 4, pp. 427-431, 1892. 



In this paper Dr. Geo. Dawson records the discovery made by 

 Mr. J. M. Macoun, on June 15, 1892, of "boulder clay" or "true 

 till" which on examination proved to be fossiliferous. Mr. 

 Macoun furnishes an interesting sketch of the leading physical 

 features of the island. The pebbles or rocks contained in the " till " 

 are chiefly of Triassic age and form part of the "Vancouver 

 Group." Numerous fragments of shells are found together with 

 foraminifera. 



Mr. Whiteaves has recognised the following foraminifera. 



1. Polystomella striatopunctata, Frichtel & Moll. 



2. Pulvinulina Karsteni, Reuss. 



3. Probably Nodosaria (Glandulina) laevigata, D'Orb. 



Dr. Dall's observations on Middleton Island had led him to 

 suppose the "clay-stone" to be Post-Pliocene and possibly 

 Pliocene. 



Dr. Dawson also found shells of Cardium blandum in the till of 

 Middleton Island and the samples of sand collected by Mr. Macoun 

 were submitted by Dr. Dawson to Mr. Ferrier and the results incor- 

 porated in the paper. 



H. M. Ami. 



