638 ME. H. H. AENOLB-BEMEOSE ON THE MICROSCOPICAL [Nov. 1 894, 



Another specimen of tuff (sp. gr. 2*54) is made up of lapilli in 

 a cement of crystalline calcite. The lapilli are of two kinds : — (a) 

 Similar to the blocks in outcrop 56, and (6) light green, almost 

 isotropic, containing globulites, or composed of the felspar-like 

 material. The vesicles are filled with calcite. 



A third specimen (sp. gr. 2-50) is similar to the preceding, 

 except that it contains lapilli of a yellowish-green glass with 

 crowds of globulites and a few felspars giving lath-shaped sections. 

 The globulites are often arranged in the form of a felspar-lath or 

 of a rhombic section. The vesicles are filled with calcite or the 

 felspar-like material with radio-fibrous structure. 



Kniveton, Outcrop 56. — Lies between Woodeaves Farm and Lea 

 Hall in a large field containing a limestone-quarry, and through 

 which the brook runs in a southerly direction. The field forms the 

 eastern side of the valley, and on the steep slopes the rock may be 

 seen in several places. In the upper part of the bed it is soft and 

 easily broken, and contains small pieces of limestone. There are also 

 included blocks of a very hard light-coloured rock, which is studded 

 with calcific and dark green amygdaloids, and in this hard rock 

 minute felspars may be seen with a lens when the rock is wetted. 



In the steep right-hand bank of the stream is a good exposure 10 or 

 12 feet high, without vegetation. It is almost entirely made up of 

 blocks more or less rounded, varying in size from 10 inches to about 

 1 inch in diameter. They appear like spheroids embedded in a fine ash. 

 When extracted, the ash adheres to their outer surface. In places 

 the ash predominates, and when broken up is found to contain smaller 

 spheroids of the harder and compact amygdaloidal rock. The ash 

 is made up of small lapilli, the amygdaloids in which are well seen 

 when the rock is wetted. Twenty feet higher in the series the ash is 

 exposed, and contains smaller and fewer amygdaloidal blocks. The 

 whole exposure is about 30 feet thick. 



A section from one of the included blocks (sp. gr. 2*72) contains 

 olivine, altered partly to calcite, and partly to a felspar-like mosaic 

 often containing pyrites. The felspar occurs in rhombic and in 

 lath-shaped sections. Some have parallel extinction and some are 

 not twinned. I have been unable to obtain twins with symmetrical 

 extinction. Three give the angles 23° and 27°, 20° and 30°, 25° 

 and 50°, referred to the trace of the plane of composition. The 

 ends are often indented, and some of the felspars contain globulites. 

 There are also microlites, which extinguish parallel to or at a small 

 angle with their length. They are sometimes curved. The base is 

 a very feebly-refracting felspathic substance, sometimes brown with 

 globulites or magnetite, arranged parallel to the sides of the olivine- 

 pseudomorphs. The amygdaloids are large, numerous, and close 

 together. The felspars near them are often arranged tangentially 

 to the almost circular amygdaloid boundary, and where the wall is 

 very narrow it is almost entirely formed of one or two felspars ; 

 see PI. XXV. fig. 6. Calcite generally fills the vesicles, and some- 

 times has an outer zone of feebly double-refracting grey material 

 whose fibres are roughly parallel to the radii of the zone. 



