626 MB. H. H. AENOLD-BEHEOSE ON THE MICE08COPICAL [NOV. 1 894, 



to calcite. The base is isotropic, and in polarized light structureless. 

 In ordinary light it is seen to be of a brown colour, with a felt 

 of crystallites. The crystallites are often curved, feather-like in 

 arrangement, and frequently sprout from the ends of a felspar-lath, 

 so that they may perhaps be referred to felspar. 



A specimen of the fragmental rock (sp. gr. 2*50) consists of 

 lapilli, some of which bave a white porcellaneous appearance. Under 

 the microscope are seen several lapilli of a rock similar to that last 

 described. Some small ones are a dense black, with a thin, light 

 yellow border; sometimes they contain a few felspar-laths. The 

 larger ones, which are black or dark brown, are cracked, the 

 cracks being filled with a light yellow material or with calcite. 

 In reflected light the brown portions look like a cream-coloured 

 porcelain, parts of which are dirty and tinged with brown (see 

 PI. XXY. fig. 3). In a lapillus one large pseudomorph of olivine 

 is present, and is composed of a yellow material and calcite. Some 

 portions of the former are dichroic, but the greater part has only a 

 faint action on polarized light. The pseudomorph is surrounded 

 by a thick coffee-brown border, with bands parallel to the boundary 

 of the olivine. The whole is embedded in the dense black matrix 

 of the lapillus, the brown and the black being part of the same 

 mass and containing a few felspars in lath- shaped sections, a felspar 

 often being embedded in both portions. Smaller similar olivine- 

 pseudomorphs occur in the thin section. The brown border and 

 black matrix appear very much like tachylyte. Altered augite 

 occurs in small crystals or prisms. There are few vesicles : the 

 larger of these are filled with calcite, the smaller with a yellow radio- 

 fibrous material. 



Brook Bottom, Outcrop 7. — This is mapped by the Survey as 

 running across Water Lane, which leads from Brook Bottom to 

 Tideslow Bake. I could only find it in the lane, where it is a 

 dolerite exposed for about 90 yards, and in an adjoining field. In 

 Brook Bottom, a valley, there is a rock exposed for a distance of 

 about 50 feet and dipping 18° about 10° W. of S. It is bedded, 

 and readily breaks into thin laminae, parallel to the bedding. It 

 consists of lapilli in a calcite- cement. The upper portion of the 

 bed crops out about 130 yards north of Highfield House, and is 

 exposed on the left-hand side of the road. 



The bed of dolerite is 30 or 40 feet above the horizon of this 

 tuff, the two being separated by beds of limestone. The tuff is about 

 20 feet thick. The horizontal section, sheet 70 of the Geological 

 Survey, passes near this place; and another bed of toadstone should 

 be added to make the section complete. 



The tuff is generally laminated, but some portions are more 

 compact and do not break up into laminse. A specimen of the 

 former (sp. gr. 2*64) consists of lapilli of a reddish colour, which, 

 as well as the amygdaloids in them, have a thin yellow border. A 

 large lapillus with very irregular outline occupies the greater 

 portion of the slide. It contains olivine in porphyritic crystals 



