396 ME. F. ETJTLEY OK ERTJPTITE EOCKS FEOM THE 



No. 3. Cant Hill, West end, at top of hill (Plate XII. fig. 2).— 

 This is a purplish-grey rock with a somewhat fissile structure and 

 little greyish- white specks of irregular form. It was derived 

 from a small quarry which has been opened out on the top of the 

 hill. The rock in this quarry is strongly jointed, and appears to 

 be fresher than that occurring in the small grubbing from which 

 the specimens nos. 1 and 2 were procured. The stone here still 

 seems, however, to be considerably weathered *. A section of 

 this rock seen under the microscope appears as a clear, almost 

 colourless, glassy lava full of small vesicles, frequently bordered 

 by minute round granules or moniliform edgings of an opaque- 

 snow-white substance. The glassy matter also contains irregular 

 nests, strings, and nebulous segregations of minute j^ellowish- 

 green granules, which appear to be epidote (fig. 2, Plate XII.) 

 The vesicles give circular and elliptical sections in some places, while 

 in others they are greatly elongated in uniform directions, sometimes- 

 occurring close together, so as to form vesicular streams, which are 

 frequently sinuous and indicate fluxion. There is also a wavy,, 

 thread-like structure in the glass, which is not very clearly to be 

 recognized except between crossed nicols under a moderately high 

 power, when the fibres are seen to depolarize in feeble greyish-blue 

 tints. At first sight it would seem that this substance might be 

 serpentine, but it is probably a felsitic ' substance (" microfelsitic- 

 basis " of Rosenbusch). In many places the glass is almost 

 unaltered. Small crystals of triclinic felspar occur in this glassy 

 or once glassy ground- mass. The rock appears to have been some- 

 what crushed, and contains a considerable amount of calcite, a little 

 quartz, and a few dark opaque grains, which are either magnetite 

 or titaniferous iron ; possibly there is a little serpentine. Much of 

 the opaque white or faintly rusty-stained matter in the section I 

 am inclined to regard as leucoxene, resulting from the complete 

 decomposition of ilmenite. We have here, then, a partially devitri- 

 fied lava of a highly vesicular character, in which the felspars are 

 triclinic, while the secondary products, epidote and leucoxene, indi- 

 cate that pyroxene, possibly olivine, and ilmenite were once present 

 as original constituents. The rock, therefore, may be assumed to 

 have been a vitreous basic lava, and may very likely be coeval 

 with the lavas erupted in the Brent-Tor district, which, although 

 mapped as occurring in the Culm series, are probably of Devonian 

 age. 



No. 4. Caoit Hill, West end, at top of hill. — ^This specimen was 

 taken from the same quarry as no. 3, which it closely resembles, 

 but shows a considerable amount of ochreous matter, which is 

 distributed in small patches and films throughout the rock. Calcite- 

 seems, however, to be absent from this specimen, and there is a large 

 proportion of serpentinous matter, so large, indeed, that by burnish- 

 ing a smoothly cut surface of the rock with an ivory paper-knife, a 

 fairly good polish can be communicated to it. 



* I would here acknowledge the courtesy of Mr. Wm. Buller, of Cant, in 

 giving me useful information concerning the quarries in the neighbourhood. 



