348 EEV. E. HILL AlfD PEOF. T. &. BONNET ON THE 



hill rocks as representative rather of the Kite-Hill than the Cadm.an> 

 group. 



(6) The Slates. 



The microscopic structure of three varieties of slate was de- 

 scribed in Part II. The structure of one of them (from the quarry 

 near Forest Eock Inn) appearing on further investigation to be rather 

 exceptional, we have examined a few more slates in the hope of ob- 

 taining some help in correlation. The only one among them which 

 presents any resemblance to it is a specimen from a locality east of 

 Grace-Dieu grounds. The peculiarity of the Forest-Kock-Inn slate 

 is that the slide with ordinary light is unusually clear, resembling a 

 glass in which a number of very minute microliths, of a pale yellowish- 

 green colour*, with some specks of ferrite, are irregularly disseminated, 

 so as to leave occasional clear interspaces ; and this base, with crossed 

 Meols, exhibits a kind of devitrified structure. The other slide has 

 very similar microliths and brown specks, a clear matrix showing 

 a similar structure with crossed Mcols, but more obviously clastic, 

 fragments of felspar crystals being in places distinct. There seems 

 to be some evidence for correlating these two rocks; but, unfortunately, 

 this does not help much, as the position of each in the series is un- 

 certain, and probably both are bounded by faults. 



In the Whittle-Hill honestone the matrix seems to be fairly clear, 

 with little earthy matter, but crowded with minute microliths as 

 above, looking as if it were composed of comminuted felspar, in which 

 occur rather larger grains of felspar and quartz. The microliths are a 

 little more wavy in outline than those in the other rocks, and assume, 

 with crossed Mcols, a golden-yellow tint. There are small clusters 

 of ferrite, associated with granules, which are probably garnet. 

 This rock has a slight resemblance to the other two. 



The specimen from the quarry west of the School House, Grace 

 Dieu, has also a slight resemblance to the above, but is more 

 crowded with yet smaller microliths, and has a good many specks of 

 ferrite or some pale earthy mineral. A flinty slate from a knoll on 

 the west side of Old-John Hill rather resembles the last. There are 

 occasional distinct felspar fragments and quartz, with grains of epi- 

 dote, which the microliths may also be. 



The slate of Beggar's T»[ook is distinctly banded ; the felspar frag- 

 ments are rather angular and sometimes long, quartz apparently 

 rare, microliths as before, but the general appearance more earthy. 

 The slate of the summit of Old- John Hill, on the whole, resembles 

 the last. The slate of Groby Quarry, which may be taken as a fair 

 example of the roofing-slates of the Forest, differs much from all 

 the above. It has the usual microliths, with a fairly uniform frag- 

 mental structure, consisting of subangular quartz, decomposed 

 felspar, grains of opacite, ferrite, viridite, and mica. The viridite, 

 like the microliths, is no doubt a secondary product ; but the mica 

 seems an original constituent. It is generally clear and gives bright 

 colours with crossing Isicols ; but occasionally it is interbanded with 

 a pale green variety. Probably a little alteration has taken place. 

 * Perhaps epiclote ; some of the darker grains are not unlike menaUte, 



