THE ORIGIN OF THE INCLUSIONS IN DIKES 3 



EXAMPLES 



(A) All inclusions near place of origin. — 



Cornwall, England: In the southern part of Cornwall, near 

 Carrick Luz, there is a gabbro boss surrounded by a fringe of gabbro 

 dikes extending outward through the serpentines of the region. 

 All of the dikes contain numerous inclusions of the serpentine. 

 These dikes also illustrate injection foliation.^ 



Da la Beche reported one of the granite dikes of this region to 

 contain numerous fragments of the slate which it cuts.^ 



Mexico: In the state of Guerrero, Mexico, a granite sill from 

 12 to 15 feet wide cuts the Juratrias shales, and contains a number 

 of fragments of the slate a foot in diameter. The vertical sill runs 

 parallel to the bedding of the shales, but has evidently broken off 

 the shale inclusions from the walls near the place where they are 

 frozen in the dike. The inclusions are now nearly weathered out 

 of the granite, so that the effect of the heating is indeterminate, 

 but the granite adjoining them shows no immediate contact 

 effect.3 



Cape Ann, Massachusetts : At Pigeon Cove, Cape Ann, is a labra- 

 dorite porphyry dike of very coarse grain, 25 feet wide and traceable 

 for 3 miles, everywhere cutting alkaline hornblende granite, but 

 including fragments of diabase and quartzite. The inclusions are 

 about 6 inches in diameter and have a subangular to rounded out- 

 line. The numerous diabase dikes now exposed in the, region cut 

 the porphyry dikes. The inclusions must have come from quartz- 

 ites and diabase dikes cutting them, forming the roof of the granite 

 batholith, and must have sunk or been carried down in the dike to 

 their present level. Since that time, which was probably the 

 Carboniferous, the quartzites from the roof of the bathoKth and the 

 upper part of the bathoKth itself have been completely removed by 

 erosion. Quartzites appear in small amounts elsewhere in Essex 

 County. • The distance through which the inclusions must have 



' J. S. Flett, "The Geology of the Lizard and Meneage," Mem. Geol. Stirv. Great 

 Britain, 1912; also, Proc. Geologists^ Association, XXIV (1913), 127. 



^ Geological Report on Cornwall (1839), p. 182. 



3 The writer is indebted to Mr. Y. S. Bonillas for this information. 



