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 26
