256 MR. H. H. ARN0LD-BEHR0SE ON [Aug. 1907, 



This account of the bedded tuffs of the northern area would not 

 be complete without a description of the tufaceous limestone of 

 Cave Dale near Castleton. Some 32 feet above the lava in Cave 

 Dale is a bed of granular tufaceous limestone about 7-J- feet thick : 

 it is denoted on the map (PL XIX) by broken lines. I have traced 

 this tufaceous limestone yard by yard round the limestone which 

 caps the lava on the northern side of the dale ; and on the 

 southern side, from a point about 400 feet south of Hurdlow 

 Plantation along the southern slope, to within a short distance 

 of Dirt Low. At the westernmost point, south of Hurdlow 

 Plantation, the tufaceous rock dips under the limestone and is 

 found on both sides of the dale. On the southern side it extends 

 for a distance of two-thirds of a mile (measured in a straight line). 

 On the northern it can only be traced for a short distance and 

 under the above-mentioned cap of limestone. Prom the top of the 

 tufaceous limestone to the summit of the hill near Dirt-Low Rake 

 there are 160 feet of limestone measured vertically. As the dip 

 of these beds is nearly horizontal, there are at least 160 feet of 

 limestone above the tufaceous rock. From these data the following 

 section has been constructed, to which are added notes on the 

 structure of the tufaceous limestone : — ■ 



Thickness 

 in feet. 



1. Limestone, at least 160 



2. Granular and oolitic limestone, with lapilli and pebbles of 



previously-consolidated limestone 3 



3. Soft, more or less laminated, tufaceous limestone, with 



waterworn limestone-pebbles measuring up to 4 inches 

 in length. The pebbles often consist of a limestone 

 similar to No. 2, and contain Girvanella 1 J 



4. Granular limestone, similar to No. 2 3 



5. Limestone ... 32 



6. Lava of Cave Dale — 



(This lava is at least 199 feet below the limestones of Dirt Low.) 



Since the tufaceous limestone can be traced to a greater distance 

 in an easterly direction than the lava, it seems clear that the lava 

 thins out in Cave Dale. 



In a quarry near Peak Cavern is a bed of sandy material with 

 limestone-pebbles. It may be a bed of decomposed tufaceous 

 limestone, but I have been unable to find any evidence to show 

 whether it is on the same horizon as the Cave-Dale tufaceous 

 limestone. It is apparently cut off by a fault from the Peak- 

 Cavern limestone. 



III. The South-Eastern or Matlock Area, including Ashover 

 and Crich. (See Maps, Pis. XX & XXI.) 



The south-eastern or Matlock area, although smaller than the 

 north-western, is similar to it in several respects. It extends 

 from Cracknowl on the north to Hopton near Wirksworth on the 

 south, a distance of about 10 miles, and from Gratton Dale on 



