TRIAS. 233 



part of the Keuper series also contains beds of hard red and grey limestone, 

 wliich are worked for building-stone and road-metal near Chew Stoke. An 

 analysis of similar rock from Litton by Mr. Horace T. Brown (1884) showed the 

 following composition :^ — 



Calcium carbonate 8o'02 



INIagnesium carbonate 272 



Iron, estimated as ferric oxide, but partly present as a ferrous salt... i 99 



Phosphoric acid (about) -02 



Matter insoluble in dilute hydrochloric acid, and soluble silica = 



clay and sand 15 '66 



100 '41 



A microscopic examination of this stone led to the conclusion that the limestone 

 was to a large extent mechanically derived from the Carboniferous Limestone. 



To the north of the Mendips the thickness of the New Red 

 series rarely exceeds 200 feet, and is generally less; here however 

 the beds are nowhere far removed from the margin of the deposit. 

 To the south of the Mendips the thickness increases rapidly as we 

 recede from the older rocks ; at Glastonbury it is estimated to be 

 over 400 feet, while at Compton Dundon its base was not reached 

 after 609 feet had been bored. The entire thickness of the New 

 Red series in this part of Somersetshire is estimated at about 800 

 feet. 



The New Red rocks of West Somersetshire and Devonshire 

 comprise a series of Marls, Sandstones, Conglomerates, and 

 Breccias, which rest unconformably on the Carboniferous and 

 Devonian rocks. Looked at in a broad way, and as indicated in 

 the coast-section between Axmouth and Teignmouth, the following 

 order of succession is applicable to the country between Porlock, 

 Taunton, and the shores of the English Channel, the beds 

 increasing in thickness from West Somerset to the coast of South 

 Devon : — 



{/ 5. Upper Marls looo to 1350 feet. 

 Upper. < 4. Upper Sandstones 200 to 530 ,, 

 ( 3. Conglomerates and Pebble-beds 70 to lOO ,, 

 Middle. 2. Lower Marls, with Sandstone 120 to 850 ,, 

 Lower, i. Lower Sandstones and Breccias 500 to 1500 ,, 



1890 to 4330 ,, 



The classification and thicknesses are taken from papers by Mr. 

 W. A. E. Ussher, to whom we are indebted for the greater part of 

 our knowledge of these strata. The coast-section is represented in 

 Fig. 35-' 



To the east of Axmouth, we meet with the Rhastic Beds, and thence trace their 

 passage downwards into the variegated marls which appear along the cliff, at the 

 base of the Greensand and Chalk. West of Seaton, we find low cliffs of Red marls, 

 which appear again at Branscombe, dipping gently to the east. Continuing 

 towards Sidmouth, the beds become less calcareous and finally quite loamy, until 



^ See also Geol. E. Somerset, etc. (Geol. Survey), p. 59. 



^ W. Whitaker, Q. J. xxv. 152 ; see also W. Pengelly, Trans. Plymouth Inst. 

 1861-65, Trans. Devon Assoc. 1863, 1866; Ussher, G. Mag. 1874, p. 163; Q. J. 

 xxxii. 367, xxxiv. 459 ; Trans. Devon Assoc. 1877. 



