GEOLOGY 



much disturbed, and their upturned edges may be seen striking at the 

 agglomerate. To the east of the vents is a small valley with its eastern 

 slopes running up to a well marked escarpment of limestone higher in 

 the series. The escarpment reaches a height of 1,000 feet above the 

 sea, and may be traced for about a mile. West of the vents a similar 

 but not so well marked an escarpment may be traced. On both sides 

 of the valley in which the vents are situate a bed of laminated tuff under- 

 lies the limestone of the escarpments. Its thickness is about 90 feet, 

 and it is made up of alternations of finely and coarsely laminated bands 

 of volcanic lapilli in a cement of calcite. This tuff was probably thrown 

 out from the vents. That the volcanic action then became very feeble 

 and intermittent is proved by the irregular distribution of minute lapilli 

 in the limestone immediately above the tuff up to a height of 1 8 feet. 

 Several small dykes of dolerite traverse the southern vent, one of them 

 being several feet in width. Near the northern boundary of the Moun- 

 tain Limestone at Castleton is a small elliptical vent which forms a slight 

 feature in the landscape. It pierces the limestones near the northern 

 slope of Cow Low. The limestones may be seen dipping about 20 

 degrees north on the north, south and west of the agglomerate and within 

 a short distance of it, so that the igneous rock undoubtedly cuts across 

 the beds of limestone. The agglomerate forms a low ridge covered with 

 grass, and is about 80 feet in length. It consists of a mass of minute 

 lapilli with included blocks of a doleritic type containing minute felspars 

 in an isotropic ground mass. The lapilli contain crystals and are seldom 

 vesicular. 



The vent near the village of Hopton presents no feature in the 

 landscape and is not separated by any difference of contour from the 

 surrounding limestones. It penetrates the upper beds of the limestone. 

 A short distance to the east and also immediately north of the agglom- 

 erate the limestones are seen dipping 10 to 20 south-east. Good 

 sections of the igneous rock are seen along the Wirksworth and 

 Carsington road, and also on the side of the road which has been cut 

 in the east bank of the ravine leading down from Via Gellia on the north. 

 The rock consists of a coarse tumultuous agglomerate composed of masses 

 of small lapilli and angular blocks of basalt and dolerite. It is pierced 

 by several veins or small dykes of a black fine grained rock enclosing 

 red coloured fragments which contain felspars and are probably small 

 pieces of agglomerate caught up by the dykes. 



Near the village of Bonsall a coarse agglomerate is exposed in the 

 banks of Ember Lane and in the field above. There is a large admixture 

 of calcareous material with the volcanic detritus. It consists of an 

 intimate mixture of limestone fragments and of volcanic lapilli. This 

 mass of agglomerate probably marks the site of a vent, though there are 

 no exposures very near to it showing the dip of the limestone. The 

 adjacent limestones consist of a quartz rock or silicified limestone from 

 which all traces of bedding have been obliterated. 



Near the village of Kniveton are several exposures of Toadstone 



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