On a Boulder of Hornblende Picrite near Pen-y-Carnisiog, Anglesey

Publisher Website
Google Scholar
Abstract
L ast summer, through the kindness of Professor Rosenbusch, I was able to examine several specimens of picrite in the Geological Museum at Heidelberg, and to study the rock in the field, near the village of Schriesheim, a few miles to the north of that town. In September I was walking with some students along the road which leads out of the village of Pen-y-Carnisiog northwards to Bwlyn (Anglesey), when I observed, in a field on the left, the fractured face of a boulder, in which a number of large crystals resembling augite, glittering in the sunlight, in a dull dark matrix, recalled at once the characteristic aspect of the Schriesheim pierite. The boulder had been broken, apparently rather recently, into three pieces, one much smaller than the other two; and its volume must have been not much less than a cubic yard. In its weathered surface and toughness under the hammer it also resembled the Schriesheim rock. In both, the larger crystals (which are often about two thirds of an inch long) contain a number of dark serpentinous-looking enclosures, giving to the cleavage-faces an interrupted lustre somewhat resembling (except in the absence of a metallic gleam) that of bastite. The Pen-y-Carnisiog rock looks a little more decomposed ; but macroscopically the resemblance between my two specimens is so great that one could believe them to have been broken from different parts of the same mass. When the Pen-y-Carnisiog rock is examined microscopically, the difference between the two is rather more

This publication has 0 references indexed in Scilit: