﻿Vol. 66.~] DYKE AT CROOKDENE (NORTHUMBERLAND). 



11 



Like the Crookdene Dyke, this one contains calcite amygdaloids. 

 In the semi-lunar sections of the glassy residues there are curving 

 forms of felspar and augite and grains of iron oxide. In one case 

 the gas-cavities are partly filled with green isotropic glass, very 

 like the material which occupies amygdaloids and forms irregular 

 patches in the Morpeth Dyke. It is less devitrified, however, being 

 strikingly uniform in colour and texture, and. isotropic except for 

 an occasional faint doubly refracting band at the margins. 



Several small aggregates of felspar, more or less spherical in shape, 

 were found in this dyke. They were prepared for analysis in the 



Fig. 2. — Colly well Dylce rock, showing elementary crystallization 

 in contact ivith felspar aggregate. 



[Magnified about 544 diameters. The felspars are clear, though somewhat 

 incomplete, and the augite is in a tufty condition, while the iron oxide 

 is unindividualized in the glass.] 



same manner as those of the Crookdene Dyke. Comparison of 

 the analytical results with those for the Crookdene aggregate 

 (p. 7) shows that the two minerals are practically identical in 

 composition. 



The crystals composing these aggregates (see PI. I, fig. 1) are 

 exactly like those of Crookdene under the microscope, though in 

 the hand-specimens they are a little finer in texture. They show 

 the same twinning, interference- colours, cleavages, and inclusions; 

 they are irregularly intergrown, some are shattered and others 



