1896.] Petrography. 297 



Thurston, E.— Pearl and Chank Fisheries of the Gulf of Manaar. Bull. No. 

 1, Madras Gov. Mus. Madras, 1894. From the Museum. 



Twelfth Annual Eeport of the Board of Control of the State Agric. Exper. 

 Station of Amherst, Mass. Boston, 1894. 



Weed, W. H. and L. V. Pirsson.— High wood Mountains of Montana. Ertr. 

 Bull. Geol. Soc- Am., Vol. 6, 1895. From the Soc. 



Winge, H.— E Museo Lundii. En Samling af Afhandlinger om de i det indre 

 Brasillens Kalkstenshuler af Professor Dr. von Peter Vilhelm Lund udgravede 

 og i den Lundske palaeontologiske afdeling af Kjobenhavds Universitets zoolo- 

 giske Museum opbevarede Dyre-og Meuneskeknogler. Andet Bind. Forste Halv- 

 bind. Kjobenhavn, 1893. 



Woodward, A. S.— On some Fish Kemains of the Genera Portheus and Clado- 

 cyclus, from the Rolling Downs Formation (Lower Cretaceous) of Queensland. 

 Extr. Ann. Mag. Nat. Hist. Ser., Vol. XIV, 1894. From the author. 



Wright, M. 0— Birdcraft. A Field Book of two hundred Song, Game and 

 Water Birds. New York, 1895, Macmillan and Co., Pub. From John Wana- 



Zittel, A. von.— Paleontology and the Biogenetic Law. Extr. Natural Sci- 

 ence, Vol. VI, 1895. 



Grundziize der Paleontologie (Paleozoologie). Munchen und Leipzig, 



1895. From the author 



Scrotal Notes. 



PETROGRAPHY. 1 



Examples of Rock Differentiation.— Yogo Peak in the Little 

 Belt Mountains, Montana, consists of a stock of massivei gneous rock 

 which breaks up through surrounding horizontal sediments, that have 

 been metamorphosed on their contact with the eruptive. A vertical 

 section through the south face of the mountain caused by a branch of 

 Yogo Creek has affored Weed and Pirsson 2 and excellent opportunity 

 to study the relations of different phases of the eruptive to one another. 

 The massive rock shows a constant variation and gradation in chemical 

 and mineralogical composition along its east and west axis which is two 

 miles in length. In its eastern portion the rock is a syenite, containing 

 pyroxene, hornblende, biotite, orthoclase, oligoclase, quartz and a few 

 accessories. The pyroxene is a pale green diopside and the hornblende 

 a brownish-green variety. The latter is thought to be paramorphic 

 after the former. In structure the syenite is hypidiomorphic with a 



1 Edited by Dr. W. S. Bayley, Colby University, Waterville, Me. 



1 Amer. Journ. Sci., Vol. L, 1895, p. 467. 



