Vol. 55.] IN THE REGION OF LOCH AWE. 477 



felspar may be scattered through the same rock, or hornblende alone 

 may occur iu porphyritic crystals. The porphyritic crystals, whether 

 of hornblende or felspar, are sometimes so packed together as to 

 form the main mass of the rock. A common structure is the 

 aggregation of felspar- and hornblende-crystals in shapes correspond- 

 ing roughly to those of the hornblende-prisms, forming crystalline 

 aggregates. Instead of porphyritic crystals of hornblende, we see 

 the outlines of hornblende-crystals, but the mineral substance itself 

 that builds up the crystal is an admixture of hornblende and 

 felspar. 



Sometimes hornblende is altogether absent, and its place is occupied 

 by chlorite. Large masses of such rock occur in the neighbourhood 

 of Loch Awe and Kilmartin. Many of them in the field can hardly 

 be distinguished from sediments occurring as a green chlorite-slate. 

 They contain zones, however, full of porphyritic felspar, when their 

 igneous character can be readily determined. The felspars occur in 

 well-formed crystals, but in many cases they are broken and jointed, 

 and their angles rounded ; yet, notwithstanding the foliated and in 

 many cases very fissile character of the matrix, they have often suffered 

 very little crushing. Some zones are literally packed with these 

 porphyritic felspars, leaving little room for the groundmass. They 

 sometimes exceed | inch in length. Calcite is often associated with 

 this type of rock, and the felspar, when it has been determined, 

 has been found to be labradorite. 



There is e^ery gradation between these chloritic and hornblendio 

 rocks. Usually in chloritic rocks a certain amount of hornblende 

 of the pale platy variety is found. Li the same mass as that in 

 which these chlorite-varieties occur, the coarsest hornblendic types 

 are sometimes observed. The hornblende is always green ; the very 

 dark hornblende is seldom or never met with in these unaltered 

 areas. 



The following slides have been selected as the most typical from 

 those examined by Mr. Teall, belonging for the most part to the 

 Geological Survey collection : — 



(4366) Ford, Loch Awe. — Pale greenish schistose rock of fine 

 grain and somewhat earthy aspect. The main mass is a schistose 

 aggregate of more or less lath-shaped felspar, chlorite, and iron- 

 ore. Here and there are some large felspars which form ' eyes ' 

 in the schistose matrix. Calcite is scattered through the rock. 



(4367) Pord, Loch Awe. —A similar rock to 4366, but containing 

 numerous idiomorphic felspars in a matrix which shows little or no 

 schistosity. The idiomorphic felspars are labradorite. Matrix of 

 more or less lath-shaped felspar, chlorite, carbonates, and iron-ores. 



(5688) IN^ear Kilmartin. — Coarse-grained, greenish, massive rock. 

 Large irregular patches of green uralitic (?) hornblende, chlorite, 

 epidote, partially saussuritized felspar, and iron-ores changed to 

 leucoxene. Epidiorite. 



(5687) Near Kilchrenan. — Dark, medium-grained, massive rock. 

 Large patches of green uralitic (?) hornblende, aggregates of 



