282 PROFS. LLOYD MORGAN AND REYNOLDS ON THE [Aug. I9OI, 



Stoddart's analysis^ also relates to this rock. He gives 57*52 as 

 the silica-percentage of an example ' taken in as pure a state as 

 possible from the centre of the quarry.' The most remarkable 

 feature of his analysis is, however, as previously mentioned, the fact 

 that he tabulates 10-34 as the percentage of potash, and only '72 as 

 that for soda. The enormous percentage of potash is scarcely 

 explicable except as an error or misprint, though it should be noted 

 that Mr. Teall refers to the possible presence of orthoclase. 



Our sections show that the felspar-laths often tend to assume an 

 approximately parallel arrangement. Although there are a few 

 crystals that are somewhat larger than the others, the Damery rock 

 resembles those from Charfield Green in not showing a generation 

 of felspars of distinctly earlier date than the laths. These, which 

 are as a rule simply twinned on the albite-type, give a maximum 

 extinction-angle of 16°, but as a general rule the angle is much 

 smaller than this. Small grains of bastite-pseudomorphs after 

 enstatite are very plentiful and evenly distributed. 



Sections show that the rock exposed by the little ponds in Mickle 

 Wood is identical with that from Damery Quarry. 



The rock exposed by the pond at the cross-roads east of Woodford 

 Green is noteworthy for the very large amount of serpentine 

 present. Some of the patches show crystal-outlines, and we believe 

 that here again the original mineral was enstatite. The included 

 quartz-grains, which occur in so many of the localities in the district, 

 are well seen in this rock, and show marked corrosion by the 

 groundmass. 



Mr. Parsons has determined the silica-percentage of the fresh 

 rock referred to as occurring in the south-western portion of Middle 

 Mill Quarry ; it is 63*5, or calculating the result to a moisture- 

 free basis, 67*08. This percentage is notabl}^ higher than that of 

 the Charfield-Green rock, but the fact is easily explained by the 

 abundance of free quartz.^ Some of these quartz-grains were 

 isolated by Mr. Parsons, who says of them 



' the clear glassy appearance, fracture with absence of cleavage, infusibility in 

 the blowpipe-flame, and absence of coloration imparted to the Bunsen flame, 

 confirm the opinion that they are quartz. Whenever they are met with all 

 indications go to show that the grains are of foreign origin, and that conse- 

 quently the rocks in which they occur are not to be regarded as dacites.' 



In most respects this rock belongs to the same general type as 

 the rest. The groundmass shows numerous small grains of altered 

 pyroxene and felspar-laths, the majority of which give a maximum 



1 Proc. Bristol Nat. Soc. vol. i (1876) p. 123. 



'■^ [Since the sending in of our paper Mr. Alfred Harker has drawn our 

 attention to the widespread character of the phenomenon of the inclusion of 

 quartz-xenocrysts in basic igneous rocks, and to two papers of his (Geol. Mag. 

 1892, pp. 199-206 & 485-88) dealing with the subject. The view which he 

 there advocates is that the quartz crystallized out, not in the basic rock in 

 which it now occurs, but in a magma of acid composition which once overlay 

 the basic. This explanation seems to fit the facts better than that which 

 regards the quartz-grains as fragments mechanically caught up by the magma.] 



