GEOLOGY 



at Cromford the limestone forms short lenticular beds in the shale. In 

 other places the limestone is intercalated in thin beds amongst the shales, 

 and the proportion of limestone to shale varies greatly. Near Ashbourne 

 the limestones are more evenly bedded, more numerous and closer to- 

 gether, so that it is often difficult to say whether they are at the top 

 of the Mountain Limestone or at the base of the Limestone Shales. In the 

 neighbourhood of Kniveton and Tissington they are often contorted. 



One of the best exposures which gives evidence of the numerous 

 folds into which these beds have been thrown was seen during the con- 

 struction of the new railway from Buxton to Ashbourne near the village 

 of Tissington. Although only about 60 feet of these shales were seen 

 in a distance of 300 yards, they were bent into about six anticlines and 

 the same number of synclines. The thin beds of limestones are local 

 and soon thin out. 



It has been estimated that these beds may reach a thickness of 

 1,000 feet in the northern part of the county, but at Matlock they cannot 

 be more than 400 feet thick. 



The sandstones in Edale which are mapped as Yoredale by the 

 Geological Survey may possibly belong to the Shale Grit. In places 

 further south they are absent, and the Shale Grit rests on the Yoredale 

 Shales. 



IGNEOUS ROCKS 



The quiet deposition of the Mountain Limestone of Derbyshire was 

 in various places disturbed by small volcanoes which poured out their 

 lavas in a molten condition or discharged their fragments of volcanic 

 detritus over the sea floor. The volcanic activity did not cease with the 

 deposition of the Mountain Limestone, but continued whilst the lower 

 portion of the Yoredale Shales was being formed. There was a later 

 phase of volcanic activity when the molten material was no longer able 

 to force its way to the surface, but intruded itself between the beds of 

 limestone or successive lava flows. 



The igneous rocks of the county for more than a century have been 

 known by the name of Toadstone. Some suppose it to have been 

 derived from the German todtstein (deadstone), from the absence of ore 

 in it ; others consider the rock was so named because of its resemblance 

 to the back of a toad. 



The Toadstones vary not only in their character and appearance 

 but also in their behaviour with regard to the limestone beds in which 

 they occur. The rock is in places hard and dark in colour, in others 

 soft and decomposed to a kind of clay. In some cases it is evidently 

 interbedded with the limestones and in others cuts across them. 



Lithologically the Toadstones may be divided into two classes, viz. 

 massive and fragmental. The massive kinds include lavas which are 

 contemporaneous with the limestones in which they occur, and have a 

 vesicular and often a slaggy appearance. The vesicles are frequently 

 filled with amygdules of calcite and other minerals. The harder, more 



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