Vol. 6$.^\ THE TOADSTONES OF DEKBYSHIliE. 245 



and also near The Holmes. In that year Mr. Samuel Moore wrote 

 a short paper, calling attention to the presence of two beds of toad- 

 stone on Cop Hound. 1 Soon after the publication of this paper I 

 went over the ground with Mr. Moore. The tracing from his 6-inch 

 map with which he kindly provided me, helped me very materially to 

 trace the effects of Moss Eake and Shuttle Rake on the outcrop 

 of the two lava-flows. 



The upper lava forms the summit of Knot Low near Miller's-Dale 

 Station, is capped by limestone on the adjacent hill above Crichley 

 Wood, and is also seen on Bole Hill, north of Tunstead. I have been 

 unable to trace it so far north-east as Smalldale, as mapped by the 

 officers of the Geological Survey, and have therefore denoted this 

 part of the boundary by a dotted line. Its greatest thickness is in 

 the neighbourhood of Miller's Dale, where it is about 100 feet 

 thick. This lava-flow was preceded by a fall of volcanic detritus. 

 The tuff is present on the northern slope of Chelmorton Low, near 

 Miller's-Dale Station, and on the lower portion of Knot Low. 

 Some years ago it was well exposed in a tram-cutting connected 

 with the limestone-quarry near Miller's-Dale Station. The following 

 section was seen by me : — 



Thickness in feet. 



Limestone — 



Lava-flow, olivine-dolerite about 100 



C oarsely-bedded tuff, at least 4 



Lava-flow, atnygdaloidal dolerite 9 



Tufaceous limestone 2 



Clay 2 



Limestone — 



[See also Quart. Journ. Geol. Soc. vol. 1 (1894) p. 631.] 



A good section of the tuff is also exposed in a quarry several 

 hundred yards east of the limekilns, near the railway-line. Until 

 a few years ago the junction of the lava with the tuff underneath 

 it, resting upon the limestone, was seen on Knot Low. 2 



The decomposed calcareous tuff or tufaceous limestone was several 

 feet thick. Resting upon it was the lava of Knot Low. The isolated 

 position and contour of the Low have suggested to some persons a 

 volcanic vent ; but it is one of those cases in which part of a lava- 

 flow forms a prominent hill. It is situated between the Wye Valley 

 and Monk's Dale. The evidence that it is not a vent is seen by the 

 limestones dipping regularly under the igneous rock on the north- 

 western and south-western sides of the hill; and in the quarry-section 

 the lava rests upon the limestone below it. On Priestcliffe Low, 

 under the lava are to be found pieces of a red rock, which is 

 probably a decomposed tuff or a volcanic mud. I have found a 

 similar material in connexion with other lava-flows of the district. 

 Under the microscope it appears as a more or less amorphous mass, 

 sometimes composed of fragments cemented together, and has no 

 recognizable structure. 



1 Geol. Mag. 1903, pp. 84-85. 



2 ' A Sketch of the Geology of the Lower Carboniferous Kocks of Derbyshire ' 

 Proc. Geol. Assoc, vol. xvi (1899-1900) pi. v, flg. 2. 



