PRECARBONIFEROUS ROCKS OF CHARNWOOD FOREST. 205 



microliths (and ? cavities). A faint green tinge runs through this, 

 like a kind of network, so that the field seems to be occupied by a 

 number of rather ill-defined roundish grains set in a duskier and 

 greener base; sometimes these almost disappear and the ground- 

 mass becomes rather streaky. "With crossed Mcols the ground-mass 

 rather resembles the last, only the doubly refracting portions are 

 less clearly defined. Many of the rounded patches disappear, giving 

 it a more streaky aspect, while those which remain become more 

 definite and angular in outline. Dusty clusters and dark grains 

 with grouped epidote are scattered about. The larger felspar crystals 

 are greatly decomposed, being sometimes almost wholly replaced by 

 epidote and viridite or by a zeolite*; still there are indications 

 that these are of clastic origin. Both kinds of felspar seem to have 

 been present ; this is confirmed by the smaller crystals, which, strange 

 to say, have escaped better. The quartz grains vary much in size 

 and form, some being less than '01 inch in diameter ; generally they 

 are roundish, but some are distinctly subangular and irregular in 

 form, one strip, which is incomplete, being quite 0*15 inch long ; it 

 is broken through three or four times. Sometimes these grains are 

 separated from the ground-mass by a sharp line of division ; but 

 more frequently it seems to melt rapidly into the quartz, so that 

 the latter is surrounded by a finely granulated band about '001 inch 

 wide. Both modes of limitation may occasionally be seen in the 

 same specimen. The quartz grains show bright colours, are sometimes 

 clear, and sometimes contain small dark microliths and cavities. 

 The question of their origin, and that of the felspar crystals, will be 

 discussed hereafter. There are one or two grains of a translucent 

 pale green mineral, with the edges and cracks (the latter sometimes 

 crossing one another roughly at right angles) defined by thickly 

 clustering black granules. The clear part contains many small 

 pore-like cavities, some apparently empty, others stained with 

 black. With polarized light the green, as before, appears to be an 

 aggregate of a chloritoid mineral. In general appearance this 

 mineral rather recalls the structure of olivine or garnet, and may 

 be a pseudomorph after one of these. 



Bardon Hill, Porphyritic Bock of Lower Quarry, north side 

 (p. 781). — In microscopic structure this rock is extremely similar 

 to the last ; but the quartz grains (which are often a little longer) 

 approach nearer to crystals in outline, and are traversed by some 

 large and very many minute cracks, the latter frequently meet- 

 ing nearly at right angles. The quartz contains some rounded 

 patches of viridite enclosing clusters of minute epidote. One or two 

 grains of the green and black mineral mentioned above are present. 

 On the whole the microscopic evidence for the identity of these two 

 rocks is very strong. 



Bardon Hill, Lower Quarry, south side (p. 781). — We have already 

 (toe. cit.) described the remarkable change in this rock as it is traced 



* For brevity we will thus designate the secondary microliths, alreadj r men- 

 tioned (p. 201), the precise nature of which we have not. yet been able to deter, 

 mine. We suspect the mineral to be orthorhombic. 



