Thos. R. Waller — Volcanic Rocks, Nuneaton. 323 



From these I have prepared a considerable number of thin sections, 

 and I propose to give here a summary of the chief conclusions at 

 which I have arrived as to the following rocks : — 



1. The Ashes. 



2. The Quartz-Felsite. 



3. The Basic rock which is seen in contact with the Quartz-Felsite. 



4. The Quartzite. 



5. The Diorite in the latter. 



1. The Ashes from the " Tunnel " at Caldecote are distinctly 

 bedded, and contain, where they are coarsest, angular grains of quartz 

 and felspar ; but in most parts the dust has originally been so fine, 

 and subsequent changes have so much veiled the components, that 

 not much can be made out as to their constitution. A light-coloured 

 specimen from this locality has an appearance and texture very 

 similar to those of a tuff from the Pentland Hills, of which I pos- 

 sess a specimen. It contains a number of rather darker grains, 

 which are not evenly distributed all over, but are gathered up into 

 a sort of network with irregular meshes, the open spaces being nearly 

 free from them. 



A few of the felspar grains are much larger than the majority of 

 the fragments of which the rock is made up ; one well-defined and 

 pretty perfect crystal measuring about ■£& of an inch, another of 

 orthoclase measures -rjro of an inch. There are occasional fragments 

 of apparently a fine-grained basalt, and in some of these large felspar 

 crystals are included, showing that the basalt was porphyritic. I 

 have seen no well-defined augite, but a few green patches give 

 rather the impression of an altered pyroxene. The quartz fragments 

 are not very frequent, and the general character of the mass is 

 decidedly basic. 



In the coarse conglomerate at the base of the quartzite, blocks of 

 ash are found, and those which I have examined are made up of 

 much larger fragments than the specimens from the Tunnel. The 

 fragments present a considerable variety of aspect ; a few of them 

 look like pieces of a very vesicular lava — basic apparently : others are 

 pale green, like some of the Welsh felsites of the Snowdon district, 

 and have the peculiar curdled or damascened appearance which has 

 been often described in these. 



2. The Quartz-Felsite. — It is only sparingly that specimens occur 

 which have the appearance of typical unaltered quartz-felsites. In 

 them the quartz and felspar occur in large grains and crystals, the 

 ground-mass forming as usual inclusions and indentations in the 

 former. In the ground-mass itself the fluidal texture is very marked, 

 and it shows the usual indeterminate polarization of the felsites. 



The felspar is much clouded by products of decomposition, but 

 there is a good deal left which allows the twinning to be made out. 

 Both orthoclase and plagioclase occur ; in the latter, frequently with 

 very fine and sharply-distinguished lamella?. 



The greater number of specimens which have a general look of 

 quartz-felsite, seem to me to have much more of the character of a 

 felsite brecciated and recemented with probably but little disturbance. 



