230 A POPULAR SKETCH OF THE 



tage at Turnditch, and at Agnis Meadow, near Kniveton. At 

 Turnditch lime quarries, there are forty feet exposed, consisting of 

 alternations of shale and limestone in beds varying from three 

 inches to three feet in thickness. The limestone is very hard, rather 

 crystalline, dark coloured internally, but light brown outside. Its 

 external appearance, when exposed to the weather, is at a little dis- 

 tance more like gritstone, and the weathered blocks are marked by 

 horizontal lines, showing an original lamination. Sometimes this 

 lamination is apparent, and the block will split into flags. Beds of 

 this kind, I believe, exist at Ashford, near Bakewell ; and I observ- 

 ed a bed of dark Umestone, one foot thick, in the limestone shale 

 which forms the bed of the brook just above Breadsall, two miles 

 north east of Derby. 



The beds of limestone in the shale increase in number and im- 

 portance, I believe, as the formation passes westward into Stafford- 

 shire : but I shall leave the further discussion of this point till I 

 come to speak of the positions and dislocations of the rocks, which 

 in this formation are very interesting. 



9. — The Mountain Limestone. 



This, the most interesting and, next to the coal measures, the 

 most important formation in the district, is so named from its fre- 

 quently forming a hilly and mountainous country. The name is 

 not a good one, as other limestones may equally form mountainous 

 countries : but as the whole nomenclature of Geology is at present 

 provisional, it is better to retain the old and generally understood 

 names, as far as possible, till a regular system of classification and 

 nomenclature can be constructed. By far the principal mass of the 

 mountain limestone is composed of carbonate of lime, sometimes in 

 rather thin and regular beds, sometimes in beds so thick and irregu- 

 lar as almost to defy the detection of the dip (or inclination) of the 

 rock, unless a very large section be exposed. Among the beds of 

 carbonate of lime, are sometimes found portions which contain mag- 

 nesia in considerable abundance ; and in some parts of the limestone 

 district there is a thick and important formation, called "dunstone," 

 which I believe to be magnesian limestone. The bedding of this is 

 often obscure ; but in some places, as on Middleton Moor, near 

 Wirksworth, the lines of stratification are very apparent. In the 

 upper beds of the mountain limestone, there is frequently a consi- 

 derable quantity of silex, in the form of chert. This occurs some- 

 times in beds, as in the quarries near Bakewell, where a bed ot 



