TEANSACTIONS OF SECTION C. 623 



Tocks. The recognisable sequence of the component strata in the several higher 

 Cambrian areas was shown, their physical relations to the underlying and overlying 

 formations pointed out, and evidences adduced in proof of the conclusion that 

 these rocks are fragments of what was originally a single continuous Upper 

 Cambrian formation, composed of corresponding members, admitting of fairly 

 satisfactory correlation with the Upper Cambrian rocks of other districts, and 

 everywhere reposing upon a great volcanic formation, of much earlier date. 



4. On the Petrography of the Volcanic and associated Eocks of Nuneaton. 

 Bij T. H. Wallek, B.A., B.Sc. 



The coarse ashes of the more northern exposures near Hartshill are made up 

 primarily of broken up quartz felsite, the minerals and fragments being cemented 

 in many places by thin fihns of a green, apparently serpentinous, mineral. 



The finer-bedded ashes by the 'Tunnel' near Caldecote contain broken felspar 

 crystals, in some cases plagioclase, in others orthoclase ; but here the dust seems 

 to have been very fine, especially at times, as some beds appear almost perfectly 

 compact. 



A little further south still, in a disused quarry, a rock exactly similar in external 

 appearance, and differing microscopically mainly in the appearing of irregular angular 

 flakes of a green serpentinous mineral, is seen in intimate admixture with a rock 

 having much of the appearance of a quartz felsite. 



This latter rock, however, has quite abnormal characters except in very few 

 places. Elsewhere the crystals are broken and angular in the majority of cases, 

 and are packed together with a very dirty-looking groundmass among them. 

 The quartz grains are in many cases crowded with very minute fluid cavities, and 

 are indented with the usual bays into which the groundmass runs, in many cases 

 connecting with almost isolated masses within the crystal. 



The felspar is to a large extent plagioclase, but is much clouded with decom- 

 position products. Some of the greenish flakes have the appearance of decomposed 

 mica. The groundmass where well developed shows good flow structure. 



Careful examination, both in the field and microscopically, suggests that the 

 andesitic rock mentioned in the next paragraph has flowed oper a broken and 

 partly disintegrated surface of quartz felsite. 



With these rocks is associated a dark rock, which on examination proves to 

 be composed of plagioclase felspar, and the decomposition products of apparently 

 augite, since a few grains of the latter still remain unchanged. Some of these 

 latter show the twinning that is usual, and also the cleavage parallel to the basal 

 pinacoid which has been described by Mr. Teall in the augite of the Whin SUl close 

 to the junction with the quartz felsite ; the rock is distinctly porphyritic, the 

 larger crystals of felspar being set in a mass of very minute felspar crystals, which 

 frequently exhibit the flow of rock in a very marked manner. The porphyritic 

 felspars give extinctions corresponding to Labradorite, or even incline to Anorthite, 

 and have many inclusions which frequently are arranged in lines parallel to the 

 length of the crystal, and are elongated in the same direction. 



At the base of the quartzite occur beds of conglomerate containing inasses 

 of ashes somewhat coarser in texture than those from the ' Tunnel ' above men- 

 tioned, and of the quartz felsite. Passing upwards, the felspathic constituent 

 gradually disappears except in one or two bands, and in the typical quartzite but 

 few grains are visible except of quartz. These show by the similarity of the 

 strings of cavities, and, in the lower beds, by the fact that the rounding to which 

 they have been subjected has not been sufficient to entirely smooth away the 

 finger-like indentations of outline, that they were derived from a quartz felsite very 

 similar to, if not actually a part of, the same mass as that previously described. 



The diorites which are associated with the quartzites are much decomposed, 

 with the development locally of a good deal of calcite. 



