500 



ME. F. ETTTLEY ON THE ECCKS 



The percentage of alkalies is, however, considerably lower than is 

 usual in rocks of this class. 



The perlitic structure is chiefly rendered evident by the massing 

 together of the minute granules already alluded to along curved 

 lines. This is indicated in the drawing which was made from a 

 spot in the section which shows the structure best, as it frequently 

 becomes very obscure, owing to the multitude of the granules, so 

 that oftentimes no arrangement denoting perlitic structure can 

 be traced. Even under favourable circumstances it is frequently 

 needful to examine the section attentively before the fact that 

 this structure is present and pervades the entire section becomes 

 evident to the observer. The specimen was collected and labelled 

 as likely to show perlitic structure. It does show it, but it is 

 the most feeble demonstration of the structure that I have ever 

 seen. It is interesting, however, as being the first indication of a 

 vitreous rock in the Malvern Range hitherto recorded, and it may 

 possibly belong to the same geological horizon as the perlitic rocks 

 of the Wrekin, first described by Mr. S. Airport *. 



The specimen is a mere surface-chip, and further search in the 

 neighbourhood from which it was derived would certainly yield 

 better material for investigation and probably more satisfactory 

 results. 



The apparent banding shown in PI. XXI. fig. 7 is merely due to 

 alteration, produced by the filtering of water along cracks resulting 

 in a slight rusting ; but these cracks, as shown in the drawing, have 

 been faulted by other minute fissures. 



No. 21. Hollybush Pass. Large Quarry on North side of road. — 

 Average sample of the stone now quarried. Very fine-grained 

 bluish-grey crystalline rock, strongly attracts the magnetic needle. 

 Under a pocket-lens it shows here and there a few scales of silvery 

 mica. Its general appearance resembles that of very fine-grained 

 whin. Under the microscope the rock appears to consist of altered 

 triclinic felspars, biotite, magnetite, and various products of de- 

 composition. The felspars, when their extinction-angles can be 

 made out, are apparently labradorite. Numerous but very small 

 apatite crystals are visible ; epidote and chlorite are present. The 

 magnetite frequently occurs in octahedra, which now and then, by 

 their reentering angles, are seen to have a parallel grouping. The 

 general impression derived from an examination of this rock under 

 the microscope is that it is a much-altered diabase. 



No, 22. SwinyarcFs Hill. Commencement of North end of the ridge. 

 — A very coarsely crystalline rock consisting of red felspar in large 

 crystals, a greenish mica in small scales, and quartz in crystalline 

 pellets, occasionally nearly half an inch in diameter. 



Under the microscope the felspars are seen to be microcline and 

 orthoclase, the former showing, in polarized light, the characteristic 

 twin-iamellse intersecting approximately at right angles, the angle 

 of maximum extinction in basal sections being about 15° from the 



Quart. Joum. Geol. Soc. vol. xxxiii. p. 449. 



