222 E. HILL AND T. G. BONNEY ON THE 



a pink felsitic rock much resembling that described above. It has, 

 however, a more distinctly crystalline ground-mass, a good deal of it 

 showing an approach to the graphic structure. There are small 

 quartz grains, but scarcely any distinct felspar crystals ; it may be 

 a branch of the above-described dyke, but there is no evidence to 

 show. 



In several places, and especially in a knoll south of Buddon Wood, 

 numerous thin veins of a pink felsitic rock occur in the granite. These 

 somewhat resemble intrusive veins, but are almost too string-like 

 and ramified to have been injected when the mass was perfectly 

 solidified. Further there never appears to be any tendency to sepa- 

 rate along the junction-surface, and this, under the microscope, is 

 not so clearly defined as in the other specimens. These veins are 

 crystallized, though more finely than the granite, and do not seem 

 to differ materially in mineral composition, except, perhaps, there is 

 little hornblende or mica. Hence it seems most probable that they 

 are contemporaneous veins, not intrusive in the ordinary sense. 



In the upper part of the great pit is a large dyke of very different 

 character, which has been traced for a considerable distance in pro- 

 cess of quarrying, running from N.W. to S.E. (in June 1877 the latter 

 end seemed to be curving more to the south) ; it is often about two 

 yards thick, but varies ; we saw no close junctions, but were told 

 that these were formerly found. At present a fissure filled with 

 breccia and rubbish is immediately above it on the north side. In 

 general appearance it is very like the Groby dyke, but slightly more 

 crystalline and better preserved ; small bright crystals, apparently 

 plagioclase, can be seen with a lens. On the floor of the pit we 

 picked up a specimen showing a good junction between the granite 

 and a rock resembling the finer variety of Groby, which also exhibited 

 the streaky flow-like structure ; probably this came from some off- 

 shoot of the main dyke, but we could get no certain information. 



Slides have been examined of both the above varieties of green- 

 stone. The coarser, in general structure, resembles that of Groby, 

 but is in rather better preservation. The felspar is clearly plagio- 

 clase ; the spaces between it are filled with viridite ; there are a good 

 many scattered grains of ilmenite &c, and some larger crystals of a 

 partly decomposed pyroxenic mineral, of which enough remains to 

 show almost to a certainty that it is an augite. The rock, then, is an 

 altered dolerite*. The finer variety shows the remains of a glassy 



* The Eev. J. H. Timins (Q. J. G-. S. vol. xxiii. p. 364) gives the following 

 analysis: — ■ 



Silica 54-39 



Alumina " 18*39 



Oxide of iron 1030 



Oxide of copper 060 



Lime 715 



Magnesia 392 



Loss on ignition 3'46 



Alkalies and loss 1-79 



100-00 

 This agrees fairly well with analyses of one of the more felspathic dolerites. 



