630 MK. H. H. A RNOLD-BEM ROSE OH THE MICROSCOPICAL [Xov. 1894, 



containing limestone-pebbles. The limestone dips rapidly down the 

 hill, and this rock disappears underneath it. I could not find the 

 tuff on the eastern side of the valley. 



A specimen of the finer-grained rock (sp. gr. 2-66) is a grey, 

 compact rock, consisting of dark amygdaloidal lapilli in a limestone 

 or calcite-cement. The lapilli are small, and are sometimes sur- 

 rounded by a dusty border. Some contain felspars often untwinned, 

 wbich extinguish parallel with their length, are almost entirely fresh, 

 and are not seldom arranged with their long axes parallel. Others 

 contain a pseudomorph of olivine, which occupies nearly the 

 whole of a lapillus. The groundmass is light green in ordinary 

 light, and isotropic. Some lapilli contain only amygdaloids, which 

 are generally isotropic. (See PI. XXV. fig. 2.) 



Another specimen (sp. gr. 2-63) consists of green and yellow lapilli 

 larger than in the preceding, with dark green amygdaloids. Olivine 

 and felspar occur as in the previously described specimen, but the 

 felspars are partly altered. There are small grains of calcite, and a 

 yellow serpentinous substance, which may be altered augite. The 

 groundmass is clear yellow-green in ordinary light, with little 

 action on polarized light. Some parts are darker patches containing 

 magnetite-dust or globulites. The rock appears to have undergone 

 alteration. Some of the vesicles are filled with calcite, others with 

 the clear yellow material, which is black or dark green in a hand- 

 specimen. This material consists sometimes of fibres radially 

 arranged, and shows a black cross in polarized light ; in other 

 portions it possesses little structure, and has hardly any action on 

 polarized light. Some of the amygdaloids are bordered with a dark 

 material, which under a magnification of 600 diameters, is seen to 

 consist of globulites. The portions in which they occur remain 

 extinct between crossed nicols. Circular patches of globulites, or 

 cumulites, also occur in the groundmass. The cement is a very light- 

 brown substance, and is composed of small granules (x600 diam.), 

 in which pieces of calcite and also pebbles of a more transparent 

 rock containing organisms are embedded. The cement of the first- 

 described specimen is similar, but contains no organisms. (See 

 PL XXV. fig. 1.) 



Ravensclale Cottage (in Cressbrook Dale), Outcrop 18.- — It is ex- 

 posed in a small cutting in the side of the hill, on the left of the 

 path, in sight of the cottages, and near the gate leading into a 

 field. The rock is very much decomposed, traversed by numerous 

 veins of calcite, and contains small pieces of limestone. It cousists 

 of red lapilli in a brown cement. Under the microscope the lapilli 

 are of a dirty-brown colour, and often altered to a brown calcite, or 

 to clear calcite with a border of iron oxide. Some of the smaller 

 lapilli are yellow, and have a feeble action on polarized light : they 

 contain no crystals. There are some vesicles filled with calcite. 

 The cement is a dirty calcite. The rock is a much altered tuff, 

 mainly composed of what were probably glassy lapilli (sp. gr. 2-48). 



