12 



HARDWICKE'S SCIENCE-GOSSIP. 



awaits him. The conspicuous headland, known as 

 the " Ness," and the estuary of the Teign will be im- 

 mediately beneath him, and his eye will range east- 

 ward, and south-eastward along the red cliffs of S. 

 Devon ; or, if he faces the other way, along the Tors 

 of Dartmoor. A less conspicuous object, but one 

 which, if he be a geologist, will have a special interest 

 for him, will be the Blackdown range, about 25*miles 

 distant, on the far side of the Exe valley upon the 

 Somersetshire and Dorsetshire border. 



Of this Blackdown rans;e, the Haldons are two 



supply is nearly exhausted) are still being cut out of 

 the hard concretionary nodules of sandstone. At 

 Haldon, however, the fossil fauna (corals excepted) is 

 comparatively poor, for out of some 200 species found 

 at Blackdown 50 only occur at Haldon. 'Whetstones 

 moreover are not quarried at the latter place at all. 

 The reason of the above facts will presently appear. 



If we examine the general structure of the country, 

 we find that horizontal beds of greensand rest uncon- 

 formably upon the edges of triassic and liassic beds 

 alike (see fig. 9). Both of the latter differ slightly to the 



Fig. 9. — Generalised Section of South Eastern Devonshire. 



TRIAS 



^ 



LIAS GREENSAND FLINT GRAVEl 



.Vertical scale about 800 feet to the inch. Distance horizontally, 

 about 30 miles. 



Fig. 10. — Ca?dium Hillamim. 



Fig. \\.—Exogyra conica. Fig.in.—T/triiellagrauulala. Fig. i^.—Pectenquadricostatus- 



Fig. 14. — Fossil 

 sponge {Si/>ho- 

 nia pyriformis). 



outliers of irregular outline. Great Haldon on the 

 north, is about five miles long, and averages about one 

 mile in breadth, while Little Haldon, separated from 

 the larger outlier by a slight depression in the Trias is 

 two miles long, and rather more than half a mile wide. 

 In ascending the hill the trias is found to extend to 

 within 80 feet or 90 feet of the summit, when it is 

 covered by about 50 feet of greensand, capped in turn 

 by about 40 feet of flint gravel. 



The greensand of Blackdown is famous for two 

 things, its abundant and splendidly preserved fossil 

 fauna, and its whetstones. The latter (though the 



eastward. With regard to the greensand it will be 

 sufficient for the present purpose to subdivide it into 

 three general portions, and to call them respectively 

 lower, middle, and upper Blackdown beds. It will 

 then be found that the lower and middle beds, which 

 contain the whetstones and the chief fossiliferous zones, 

 have thinned out to the westward, so that only the 

 upper beds are found at Haldon. The upper beds 

 themselves have however rather increased in thickness 

 westward, and include a coral zone in their upper 

 portion not found at Blackdown. This fact, together 

 with the greatly increased thickness of the flint gravel,, 



