THE ORIGIN OF THE INCLUSIONS IN DIKES 9 



also in the proportions of the rock types represented among them, 

 is a perfect agreement between the Almesakra conglomerate and the 

 pebble-diabase." It should be noted, however, that the Almesakra 

 series is now present only near Brevik. A former extension of the 

 series for 90 miles south, to Karlshamn, may have existed. 



Cripple Creek, Colorado: At Cripple Creek a number of 

 phonolite and rhyoHte dikes include or are capped by loose con- 

 glomerate and volcanic breccia. These phenomena have been 

 described by G. H. Stone^ who has confounded the origin of the 

 conglomerate and breccias with that of the dikes. As pointed out 

 by Ransome and Lindgren,^ the former are stream gravels and 

 volcanic breccias, some of which have been invaded by dikes. . It 

 appears probable that the inclusions in the dikes themselves have 

 fallen in from the overlying loosely consohdated beds. 



At Grizzly Peak, Colorado, similar granitic breccias have been 

 reported by G. H. Stone^ and it is probable that here also stream 

 gravels or volcanic breccias have been invaded by dikes. 



The manner in which an igneous rock invades a conglomerate 

 is well illustrated in a satellitic stock of the Bayonne batholith in 

 the Selkirk Mountains, British Columbia, as described by R. A. 

 Daly.'* The granitic magma has eaten its way into the conglom- 

 erate, 



dissolving out the cement in large amount, and has thus not only thoroughly- 

 impregnated the conglomerate with the granitic material, but has quite 

 separated many of the larger quartzitic pebbles, which, still rounded, are now 

 completely inclosed in granite. The cement was evidently more soluble in 

 the magma than were the quartzite pebbles — a conclusion to be expected in 

 view of the fact that the heterogeneous cement has a lower fusion-point, and 

 in relation to the acid granite, a lower solution-point of temperature, than 

 the' more highly siliceous quartzite. The partial absorption of the conglom- 

 erate must have taken place when the magma was (because cooled down) 

 sufficiently viscous to allow of the suspension of the blocks and pebbles. At 

 an earlier period, when the cooling was less advanced, the quartzite pebbles 



'The Granitic breccias of the Cripple Creek Region," Anier. Jour. Sci., Ser. 4, 

 V (1898), 21-32. 



^ U,S. Geol. Surv., Professional Paper 54. 

 ^ Amer. Jour. Sci., Ser. 4, VII (1899), 184-86. 



4 "The Geology of the N. A. Cordillera at the 49th Parallel," Can. Geol. Surv., 

 Memoir 38 (1914), p. 300. 



