244 MR. H. H. AENOLD-BEMEOSE ON [Aug. I907, 



to Ashbourne), at which place it thins out. I have been unable to 

 trace it in an easterly direction from Litton Mill to Cressbrook Mill 

 as mapped by the Geological Survey, and conclude that it is cut out 

 by a fault west of Litton Mill which we may call the Litton- 

 Slack Fault. East of the fault, on both sides of the dale, the 

 beds consist of thin limestones with chert. It is interesting to note 

 that while the Geological-Survey map makes this lava continuous, 

 from Litton Mill to Cressbrook Mill, the section along the Midland 

 Railway between Monsal Dale and Buxton 1 shows a rapid thinning- 

 out of the toadstone near Litton Mill. Since I mapped the Litton- 

 Slack Fault and before finally revising this paper, I have had the 

 pleasure of going over some parts of the ground with Mr. T. F. Sibly, 

 who is examining the Mountain Limestone of Derbyshire. His 

 observations confirmed mine, namely, that there is a fault at Litton 

 Slack. 



Our conclusions may be summarized as follows : — 



In Miller's-Dale Quarry the upper lava is succeeded by about 120 

 feet of massive limestones, the latter being overlain by thinly-bedded: 

 limestones with chert. At the western end of Cressbrook Tunnel 

 and at both ends of Litton Tunnel, thin cherty limestones are seen, 

 to rest conformably upon massive limestones (the beds are nearly 

 horizontal throughout this part of the section). The massive lime- 

 stones exposed on the railway at Litton Tunnel are the same beds 

 as those that are seen in Miller's-Dale Quarry, and therefore overlie 

 the upper lava. The junction of the thin cherty limestones and the 

 upper lava, seen in a cutting west of Litton Tunnel, is obviously a 

 faulted one. A fault with a downthrow to the east of over 200 feet 

 has thrown the lowest beds of the cherty-limestone series against 

 the lowest part of the upper lava, and has brought the massive 

 limestones of Miller's-Dale Quarry down to the railway at Litton 

 Tunnel. The officers of the Geological Survey apparently did not 

 recognize this fault, but considered that the true horizon of the 

 upper lava was at the base of the cherty-limestone series, the non- 

 appearance of the lava at Litton Tunnel being attributed to a rapid 

 eastward thinning-out of the lava-flow. We find, therefore, that 

 massive limestones about 120 feet thick occur in sequence between 

 the upper lava and the cherty-limestone series, and that the upper 

 lava is about 120 feet lower down in the series than was estimated 

 by the officers of the Geological Survey. 



The upper lava may be traced west of Litton-Slack Fault along 

 the western slope of Hamerton Hill, across Litton Dale, through 

 the village of Tideswell, by Summer Cross and Cross Gate to Wall 

 Cliff, where all traces of it are lost. It is seen again at The Holmes 

 north of Shuttle Rake ; and, except for a short distance, where it is 

 cut out by two faults connected with Moss Rake, can be traced in 

 a northerly direction, by Cop Round to Old Moor, a little over a 

 mile south of Castleton. 



Previously to 1903, I had traced this lava as far as Wall Cliff 



1 Geol. Surv. Mem. ' North Derbyshire ' 2nd ed. (1887) pi. ii. 



