266 ME. H. H. AENOLD-BEMEOSE ON [Aug. I907, 



210 feet. 1 It is probable that, owing to the dip of the beds, this 

 distance was more than its thickness at right angles to the bedding. 



The tuff is laminated, and contains fragments of chert, of lime- 

 stone often rounded, also blocks of amygdaloidal dolerite, and is 

 traversed by veins of calcite. The matrix is composed of lapilli, 

 cemented with volcanic dust and calcite. 2 



The Ashover Tuff is the only exposure of toadstone that occurs 

 outside the area of the maps which illustrate this paper. As my 

 mapping of the tuff almost coincides with that of the Geological 

 Survey, I cannot do better than refer to the 1-inch Geological- 

 Survey map, Sheet 82, S.W. According to Mr. '"Wright, 8 



' In the clearly dissected anticline of Ashover between 150 and 200 feet of the 

 upper, beds of [the] Carboniferous Limestone are exposed.' 



The Ashover Tuff would, therefore, appear to be either on the 

 same horizon as the upper lava of Matlock, or some 50 feet 

 below it. As no tuff has been found associated with the upper 

 lava, it seems most likely that the Ashover Tuff is in no way 

 connected with the igneous rocks of the Matlock area, and that it 

 may have been ejected from a vent in the neighbourhood which 

 has not been exposed by denudation. 



Crich-Hill Lava. — In the inlier of Mountain Limestone upon 

 which the village of Crich is situated, the toadstone has been found 

 in the course of mining operations at depths varying from 180 to 

 480 feet. The depths vary with the dip of the limestone and with 

 the position of the mines on the hill. Previously to 1890, I visited 

 the Wakebridge Mine to examine the toadstone. In company 

 with Mr. Benjamin Spencer I descended about 420 feet by means 

 of ladders. We then reached a level which is about 1000 yards 

 long, and passes through limestone-beds dipping 45° westward 

 or south-westward and toadstone. After passing the centre of 

 the dome of limestone we reached the same bed of toadstone as 

 that in which lead-ore was being worked. The rock is an 

 amygdaloidal lava, very much decomposed, and is evidently con- 

 temporaneous with the limestone. 



According to the Geological-Survey Memoir (' Worth Derbyshire * 

 2nd ed. 1887, p. 82) the lava is about 60 feet thick, and is covered 

 by about 370 feet of limestone. 



The absence of an upper lava at Crich points to the thinning- 

 out of the Matlock flows in an easterly direction ; and, as the lower 

 lava of Matlock is 250 feet down in the series, it would appear 

 that the Crich lava is on a lower horizon. 



IV* The South- Westeen oe Tissikgton Aeea. 

 (See Map, PI. XXII.) 

 The toadstones in the neighbourhood of Tissington represent 

 the latest efforts of volcanic action contemporaneous with the 



1 Geol. Surv. Mem. < North Derbyshire' 2nd ed. (1887) p. 154. 



2 Quart. Journ. Geol. Soc. vol. 1 (1894) pp. 639-40. 



3 * Summary of Progress of the Geological Survey for 1904 ' 1905, p. 9. 



