Dr. Berger on the Isle of Man, 41 



Third variety. Granular quartz forms the basis of it, in which 

 are interspersed some small grains or nodules of transparent quartz, 

 and some specks of white mica. 



The Fourth and last variety, is a granular quartz over-run by- 

 veins of the same substance. There are in it but a few specks 

 of mica. 



The grey-wacke of St. Ann's-head is distinctly stratified, the 

 planes of the strata being quite even, a mode of structure which 

 originates from an accumulation of specks of mica, which render 

 the rock readily fusible into a brown-greyish enamel, while it is 

 infusible in those parts where the mica is wanting. 



Along the shore between Kirk-michael and Peel-town, the 

 grey-wacke is rather thick-slaty, traversed by slender and parallel 

 veins of white quartz, coeval with the rock itself since they occur 

 along the seams of stratiiication. The mean specific gravity of 

 seven specimens of grey-v^racke is 2.702. 



C. Fla^t%-Rocks. 



"f Limestone. 



It would seem as if the appearance of the limestone was con- 

 nected with the absence of the exterior line of mountains on the 

 eastern side of the South Group. We trace it from Cass-ny-Hawin 

 River to Purl-Keill-Moirrey (Langness-point excepted) but it never 

 reaches to any elevation on the slope of the mountains ; it is 

 confined to the shore or its vicinity. 



It lies conformably over the most superficial of the produced 

 strata of grey-wacke, but the dip becomes less as the strata retreat 

 farther back from the land into the sea. It may be comprehended 

 between 10°. and 20°. 



Vol. [I. F 



