A HISTORY OF DERBYSHIRE 



dolomitic limestone to a calcareous sandstone. The former is some- 

 times burnt for lime and the latter makes good building stone. Though 

 it is difficult to say to what part of the series certain beds belong, there 

 seems to be no doubt that in the neighbourhood of Mansfield the 

 dolomitic limestones are above the calcareous freestones. 



The published chemical analyses show that the white and red sand- 

 stones of Mansfield differ from the Magnesian Limestones of Mansfield 

 Woodhouse in the amount of silica they contain, and also in the propor- 

 tion of carbonate of lime to carbonate of magnesia. 



The limestones examined under the microscope are seen to consist 

 of more or less well defined rhombohedra of dolomite, with a few angular 

 grains of quartz. In the sandstones, on the contrary, the angular grains 

 of quartz are more numerous and form in the specimens examined by 

 the writer about one-fourth of the whole rock. The sandstones may 

 therefore be termed dolomitic sandstones or quartzose dolomites. 



Sometimes the Magnesian Limestone forms scenery somewhat 

 resembling that of the Mountain Limestone district. The short ravine 

 known as Cresswell Crags has been cut through this limestone. The 

 light yellowish brown rocks are massive and jointed and penetrated by 

 large fissures and caverns. The cliffs are 50 to 60 feet in height. 

 Above the Magnesian Limestone are marls and sandstones which are 

 only found in two small outliers to the west of Cresswell village. They 

 consist of sand interstratified with marl, and are used for brickmaking. 



TRIAS 



The name Trias was given to this group of rocks on the continent 

 because they were divisible into three members. The middle one, which 

 is called Muschelkalk on the continent, is absent in Great Britain ; so 

 that here the system consists of two members only, viz. the Bunter and 

 the Keuper. In Great Britain the Triassic and Permian strata bear so 

 general a resemblance to one another that the old writers on geology 

 placed them in one group under the name ' New Red Sandstone,' Old 

 Red Sandstone being the name applied the Devonian series, which lies 

 underneath the carboniferous rocks. The marine fauna of the Trias is 

 almost entirely unrepresented in Great Britain, and it is considered that 

 the strata were deposited for the most part in great salt water lakes. 



The lower Trias or Bunter in Derbyshire consists of the pebble 

 beds or conglomerate and the Lower Mottled Sandstone, the Upper 

 Mottled Sandstone being absent. It is found in several isolated patches. 

 At Ashbourne and Mapleton there is a narrow strip which extends from 

 near Church Mayfield on the west by Bradley, Turnditch and Mugging- 

 ton to Quarndon near Derby on the east. Another strip lies south of 

 this and is cut off from it by the Snelston and Osmaston fault. It extends 

 from Norbury on the west by Edlaston and Osmaston to Brailsford. It 

 also occurs near Breadsall and Morley, Dale, and at Sandiacre in the 



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