E. B. Taxmey — Woodwardian Laboratory Notes. 551 



enough, remains to show their general fluiclal arrangement. There 

 is similarly amorphous base between the crystals, partly globuliti- 

 cally devitrifiecL Calcite aggregates and scattered specks are distri- 

 buted through the ground, and permeate the felspars. Of horn- 

 blende there is nothing left but small shapeless patches of chloritic 

 material. Magnetite grains occur throughout the ground. This 

 rock is evidently a porphyrite of the same type and composition as 

 the blacker one above described. 



Carn Boduan, from the base on south side near the turnpike. — 

 The rock here is a fine-grained grey rock weathering brownish-grey. 

 This is from the same spot as Dr. Hicks's specimen [Q.J.G.S. vol. 

 XXXV. p. 305], collected in 1878. It is somewhat less decomposed than 

 the last, but has much the same structure. The ground is micro- 

 crystalline, with interstitial glassy base ; it consists of plagioclase 

 microprisms, the extinction on each side of the twin boundary 

 measured in some cases as 3°-4° ; the parallel arrangement is not 

 so marked as in the last case. The microprisms preserve their 

 twinning better than the larger plagioclase crystals, which are 

 partly changing into calcite by patches, in which cleavage is some- 

 times developed. There are also aggregates of calcite in the ground. 

 No hornblende has escaped decomposition ; some chloritic patches 

 beset with magnetite indicate its existence, but generally the viridite 

 or chloritic matter shows no definite shape, and is almost apolar. 

 Magnetite grains as in the other cases. 



The rock at the summit of Carn Boduan has the same appear- 

 ance as that at the base, being a fine-grained grey rock weathering 

 brownish-grey. I found it at the summit inclosing a dark black- 

 grey piece of a different rock, looking like a jDiece of shale which, 

 had been converted into a sort of lydianite. This specimen was 

 sliced and examined with the microscope. .Its outline is sharp such, 

 as an inclosure would have. 



Under high powers the numerous closely-crowded brown particles, 

 which look half opaque, are broken up into aggregates of yellow 

 scales which seem to be epidote, together with black-brown grains, 

 which are magnetite changing into a higher state of oxidation ; 

 between are very minute grains of quartz. There are also some 

 angular brown dichroic scales about -gV mm. which seem to be mica. 

 The square magnetite grains and the rounded yellow scales are from 

 2^0- mm. to a little over xoT)- mm. on an average. Under a power of 

 50 diameters, in which these details are not to be seen, numerous 

 groups of epidote crystals are seen scattered through the rock, and 

 also minute garnets of about xr i^ii^. ; there are also smaller garnets 

 visible with high powers, so that they in size vary from x^.- mm. to 

 xio mm. ; they inclose magnetite particles. It seems probable tbat 

 this is an inclosed fragment, in which garnets, etc., have been pro- 

 duced by the contact-action of the porphyrite. 



The rock immediately inclosing the said fragment has the same 

 microscopic characters as that from previously described parts of the 

 hill : the plagioclase microprisms are here set parallel to the line of 

 contact. Much secondary epidote is developed, this and viridite are 



