426 THE AMERICAN NATURALIST. [Vor. XXXV. z 
surface, must necessarily be incomplete. For this reason the suc- 
cession of lavas in any district should be studied with reference to 
its general features rather than to its details, and care must be taken 
to exclude from the discussion the intermediate rocks formed by mix- 
ing of the different types. 
The great batholite forming the height of land between the high- 
land mountains south of Helena and Butte, Montana, is composed 
of rocks presenting a wide variation in composition. The main 
rock is a hornblende-granite (I) resembling closely a quartz 
monzanite. At Butte the rock is a little more basic (II). Great 
masses of aplite (III), possessing often a lenticular shape, are 
associated with the granites, perhaps as a differential product of 
the hornblende-granite, the Butte granite being the more basic 
differentiate. At the periphery of the batholite basic dikes penetrate 
the surrounding sedimentaries. 
SiO, TiO, AlO Fe,0; FeO CaO MgO K,O NaO H,O Various Tot. 
I. GT 48 15.00 Lr XT 53448 194 - 482 ; 2.76 DEI EU 
II. 64.03 15.58 1.96 2.83 4.20 2.15 4.11 2.76 
III. 77.05 12 12,84 +56 -14 57 tr 5.52 2.81 4 mcr 
As the result of his studies on the igneous rocks of the Bohemian 
Mittelgebirge, Hibsch? concludes that the succession is as follows : 
(1) flows of basalt, preceded by phonolite in a laccolite mass, (2) 
flows of tephrites, stock intrusions of essexite, dikes of camptonite, $e 
monchiquite, bostonite, gauteite, and sodalite-porphyry, (3) basalts, — 
trachytes, phonolites, and dikes of tinguaite and eleolite-porphyty- i 
Hackman? has reéxamined the ijolite in the Parish of Kunsamo, 
Finland. He finds the main portion of the several massifs to con- 
sist of the normal rock (I), but in addition to this he recognizes 
also the following as differentiation products — a nepheline-rich 
ijolite (II), a soda sussexite (III), a magnesian essexite (IV), and a T 
pyroxene-syenite which may, however, be a rock formed by the solu- — | 
€ of the granite surrounding the igneous rock in the magma ofthe — 
atter. - t 
SiO, TiO, ALO, FeO, FeO MnO CaO MgO NaO KO Pis TUM 
I 4289 10$ 1945 $34 509 ^.39 1699 374 10039 d] T LLL 
ür 4402  .63 -24.63 3.59 2.17 547 1967 143: 499 M a 
+ 47:43 mo sbo . 4.65 1.20 4 67 15.08 | 2.00 di 
IV..45.66 2.75 1104 3.57 ‘10.61 9.11 11.08 2.60 -44 — í 
1 Weed, W. H. Journ. of Geol., vol. vii, p. 737: 
? Min. u. Petrog. Mitth., Bd. xix, 
3 Bull. Com. Geol. d. Finlande (1 
. 488. 
goo), No. II. 
