Vol. 60.] QUARTZ1TE-DYKES IN MOUNTAIN-LIMESTONE. : »71 



the pipes was frequently re-crystallized, and flakes of mica were 

 abundant. There was no doubt that the pipes had been rilled 

 in from above. There were, however, certain features in the 

 Snelston outlier which appeared to present a parallelism to those 

 dyke-districts described by Diller, Crosby, and others, in which the 

 dykes had been filled by hydrostatic pressure from below ; then, 

 Snelston was very near a minor earthquake-centre, and had clearly 

 been subjected to pressure resulting in a fracturing or buckling 

 of the strata. He suggested that the Author might notice whether 

 the mica-grains were lying parallel to the sides of the dykes, or at 

 right angles to them : for it had been indicated by the American 

 investigators that the former position was characteristic of dykes 

 filled from below, while the latter position was the rule in dykes 

 filled from above. 



The Author thanked the Fellows for their reception of his paper. 

 He thought it more likely that the sandstone had been introduced 

 from above, than through several thousand feet of limestone from 

 below. Although the sand might possibly be of Millstone- Grit age, 

 the presence of Keuper Sandstone in the immediate neighbourhood 

 of the limestone-inlier probably indicated the true source of the 

 sand. 



The pits in the limestone filled with sand, shale, and Bunter 

 pebbles, mentioned by the previous speaker, were very different 

 from the dykes or veins described by the Author. He hoped that 

 the facts described in his paper would one day be useful to some 

 geologist, who would be able to explain satisfactorily the origin 

 of sandstone-dvkes in sedimentarv rocks. 



