456 



Mr. Austen on the 



Fig. 8. 



Jointed structure, New Red Sandstone near Sidmouth. 



Fig. 8. represents the north and south joints, at the intervals of 12 ft., 14 ft. 8 in., 18 ft. 10 in., 2 ft. 6 in., 

 and 12 ft. These two plans, taken only a short distance apart, give the divisional structure of the de- 

 posit. Now the dip of the beds is N.E., but from the direction of the coast at this particular place, 

 the east inclination only is seen, and consequently only one set of joints, viz. the north and south, can 

 have their vertical course observed. It fortunately happens that every one of these north and south lines 

 can be traced to the foot of the cliffs, and are there seen to meet other lines which traverse the entire 

 thickness of the deposit. The direction of these lines is from vertical to 8° or 10° E. ; it necessarily happens, 

 therefore, that such lines, if prolonged, must approximate or cross, which accounts for the various 

 distances observed upon the beach between the north and south lines. Hence it is evident that the new 

 red sandstone is structurally composed of octohedral masses, having their major axes much extended 

 through the thickness of the deposit. At the point where fig. 7. was taken, there is a subsidence of a few 

 inches to the west. 



Guided by analogy, geologists have concluded that the jointed structure of sedimentary rocks has 

 been superinduced by the agency of heat, and if the divisional lines of the new red sandstone have been 

 so produced, the same agent would account for the other phaenomena. The depression of the new red 

 sandstone so as to admit of the accumulation above it of the whole of the cretaceous and tertiary series, 

 placed it under conditions of temperature quite adequate for the purpose ; for, from the decomposition of 

 the water which the rocks would naturally contain, the oxygen would enter into combination with the 

 iron, so abundant in the deposit, and form a peroxide, except where, the same causes producing a decom- 

 position of the surface of the limestone fragments, a carbonate of iron would result ; the quantity of the 

 carbonic acid overcoming the stronger affinity of the iron for the oxygen. 



At the southern extremity of Great Haldon, near Ugbrook, also in the valley of 

 the Teign, the neighbourhood of Torbay, and everywhere along its western outline, 

 the new red series rests on the edges of the older carbonaceous or graywacke rocks. 

 About Newton, between Berry and Torquay, and between Newton and Totness 

 (Bowbridge), conglomerates and sandstones of this age fill deep valleys, as if the 

 slate rocks had presented great inequalities of surface before the newer formation 

 was superimposed. 



