262 SCIENCE PROGRESS 



assemblage of rocks in any given area of the earth's surface may 

 range in composition from quite basic to very acid types, they 

 usually have chemical characters in common which place them 

 in a definite series. Thus, for example, the whole chain of the 

 Andes in South America and the corresponding coast-ranges 

 (the Sierra Nevada, etc.) and the main chain of the Rocky 

 Mountains in the Western States of North America are charac- 

 terised by the occurrence of rocks belonging to the calc-alkali 

 series, namely, granodiorites and diorites among the plutonic 

 rocks, and their corresponding volcanic equivalents, the ande- 

 sites ; while the hill-ranges east of the Rockies (in Montana and 

 other Central States ] ), and of the Andes {e.g. in the Argentine 

 and Paraguay) present types progressively rich in alkalies. 

 Again, over large areas of the eastern portion of the African 

 Continent and in the adjacent islands, the prevailing types 

 belong to the alkali series. 2 In smaller areas, well named by 

 Prof. Judd 3 petrographical provinces, the prevalence of types 

 belonging to a definite series is also shown. Thus the Kola 

 Peninsula 4 and New England 5 may be quoted as examples of an 

 alkali-province. On the other hand, no better example of 

 the occurrence in a limited area of members of the calc-alkali 

 series can be given than the plutonic complex of Garabal 

 Hill, near Loch Lomond, 6 which comprises a rock series 

 ranging from hornblende-biotite-granite through tonalite 

 and diorite to peridotites, or that of the Loch Dee mass 

 in the Galloway area (granodiorite, tonalite, and diorite), 7 or 

 again the rocks composing the Brocken granite massif in 



1 Pirsson, "Petrographical Province of Central Montana," Amer. Journ. of Set. 

 vol. xx. 1905, p. 36. 



- Lacroix, " Les roches alcalines caracterisant la Province pe"trographique 

 d'Ampasindeva,"iV(9«?/. Arch. d. Museum, 4 me ser. vols. iv. and v., Paris, 1902, 1903. 

 See also an interesting paper on this subject by G. T. Prior, " Comparison of 

 Volcanic Rocks from the Great Rift Valley with Rocks from Pantellaria, the 

 Canary Islands, Ascension, St. Helena, Aden, and Abyssinia," Journ. of the Min. 

 Soc. vol. xiii. 1903, p. 228. 



3 J. W. Judd, "On the Ancient Volcano of the District of Schemnitz," Q.J.G.S. 

 vol. xxxii. 1876, p. 292. 



4 W. Ramsay and V. Hackman, " Das Nephelinsyenitgebiet auf der Halbinsel 

 Kola," Fennia, vol. xi. No. 2, Helsingfors, 1894. 



5 H. S. Washington, "The Petrographical Province of Essex County, Mass.," 

 Journ. of Geo/., vol. vi. 1898, p. 787. 



6 Dakyns and Teall, Q.J.G.S. vol. xlviii. 1892, p. 104. 



7 Loc. cit. 



