OBEEMITTWEIDA CONGLOMERATE. 29 



Two specimens *, from what Prof. Hughes describes as the inner 

 part of the fold, are especially interestingt. One resembles a greenish 

 grit, with marked " sheen surfaces " ; part of the slab is composed of 

 very minute materials, looking like a kind of argillite or " indurated 

 silt," the rest of small fragments, which evidently are much com- 

 pressed and elongated ; the rude cleavage-faces in the latter are more 

 " sheeny" than the more level faces in the former; the finer-grained 

 part consists mainly of granules of quartz and minute fiakes of 

 greenish, nearly colourless mica ; the coarser part of grains of quartz, 

 of felspar (less common), of flakes of greenish and sometimes white 

 mica, with little fragments of a fine-grained quartz-schist, of quartz- 

 ite or vein-quartz, and of a darkish mica-schist, not so coarsely 

 crystalline as the gneiss described above, but more so than any part 

 of the matrix. Here, although the fragmental character of the rock 

 is indubitable, no part, from the coarsest to the finest, seems to be in 

 the condition of an ordinary Palaeozoic greywacke. The edges of all 

 the quartz fragments are more or less ragged, the mica flakes are 

 generally more regular in outline than is usual in a greywacke, 

 even when it has undergone compression, and the smaller quartz 

 granules form a kind of " paste " in which the mica seems to be im- 

 bedded, more as described in the case of the contact- metamorphism at 

 Morlaix. In regard to the larger quartz grains, I feel sure that I 

 occasionally detect enlargement. Altogether I cannot doubt that 

 this is an altered greywacke, and think the alteration cannot be 

 wholly the result of pressure-metamorphism. The second specimen 

 is a schistose micaceous rock, much corrugated, with a mica- 

 ceous sheen on the surfaces of all the laminae displayed on 

 fractures, but not composed of flakes distinguishable with an ordinary 

 lens. When I examined it macroscopically, I felt uncertain whether 

 it would prove to be simply a " pressure-schist," like one of those 

 from Morlaix, or would resemble one of the more minutely crystal- 

 line schists of Anglesey or of the uppermost group of the Alps. It 

 had, however, a rather more " crystalline " aspect than I have yet 

 seen in any Palaeozoic argillaceous rock, when aff'ected by pressure 

 only. This proves to be the case on microscopic examination. The 

 principal constituent is a mica, varying from pale olive-green to 

 colourless, but usually tinted, with interstitial quartz. The mica 

 flakes are often about -007" in length, but many are smaller. There 

 is also a fair amount of a mineral, more distinctly green, in some- 

 what irregular scales, often associated, which has little, if any depolar- 

 izing action, and is no doubt one of the " viridite " group ; besides 

 this we have ferrite and opacite in variable amounts, the former some- 



* This paragraph lias been inserted since the paper was read. The speci- 

 mens which it describes, owing to an accidental misunderstanding, were not 

 seen by me until the evening when Prof. Hughes's paper was read ; they also 

 appear to me of considerable interest. He exhibited at the same time some 

 specimens of crystalline rocks (gneisses, or schists, and a marble) from the 

 district near Obermittweida ; these, I may remark, were such as, from my ex- 

 perience in other districts, I should have expected to find associated with, or 

 not far from, a gneiss such as that which occurs at Obermittweida. 



t See figure on p. 22 ; the first is (b), the second (a) of Prof. Hughes's section. 



