GEOLOGY 



marly limestone bands and blackish clays. In the boring east of Uplyme 

 the black shales seem to be very much thicker, perhaps 40 feet, and 

 the overlying white lias limestones are about the same thickness as at 

 Culverhole. Rhastic beds are at the surface in the valleys north of 

 Uplyme, bounding the Lias, and in three inliers in the valley of the 

 Axe, and fringing the Cretaceous rocks of Dalwood and Membury. 



LOWER LIAS 



Through the denudation of the Greensand Lower Lias is at the surface 

 in the valley of the Yarty north of Knap Cops ; in the valley of the 

 Axe between Membury, Hawkchurch and Axminster ; and in the Up- 

 lyme valley. Jukes-Browne estimates the thickness in the boring east of 

 Uplyme as ' probably ' 62 ft. 4 in. From Pinhay Bay eastward the 

 four zones, into which the interbedded limestones and shales of the 

 Lower Lias have been divided, are encountered in ascending series.' The 

 basement zone of Ammonites planorbis estimated at from 22 to 24 feet in 

 thickness commences with thin shales full of spines of Echinoderms. 

 The next zone characterized by A. angulatus is about 24 feet ; the over- 

 lying A. bucklandi zone about 38 feet, and the zone of A. semicostatus 

 about 1 9 feet. 



CRETACEOUS 



The Greensands are capped by faulted masses of Chalk near Mem- 

 bury and Wilmington. The chief extension of Chalk is along the 

 coast between Lyme Regis and Salcombe Mouth. Jukes-Browne pre- 

 fers the term Selbornian for the so-called Upper Greensand of Devon- 

 shire, as this term includes Greensand, Malmstone and Gault clay, where 

 typically developed in descending order, but clays or marl like Gault may 

 occur in the highest stages. 



The clayey beds found near the base of the formation at Culverhole, 

 in the South- Western Railway tunnel east of Honiton (north of OfF- 

 well), and south-east of Dalwood Common, perhaps also on Shute Hill 

 (where the chert-beds are exposed), may be equivalent to the Malmstone 

 or Upper Gault (zone of A. rostratus) in Jukes-Browne's opinion. Five 

 shafts were sunk in the construction of the tunnel east of Honiton." In 

 the three westernmost of these clay with chert (resting on chert beds, 

 broken up but perhaps partly in situ) from 33 to 54 feet in thickness, 

 overlies the following succession : — 



ft. ft. 



Grey sand with springs from 62 to 96 



Yellow sand, very wet „ 1 8 „ 20 



Gault clay, blue and brown „ 6 „ 7 



' Black sand „ 40 „ 50 



Layer of white sand i 



Sandy clay „ 10 „ I2 



* Sluart. Journ. Geol. Soc. 1902, vol. Iviii. pp. 280, 281. 



* Jukes-Browne, 'Cretaceous Rocks of Britain,' Mem. of Geol. Sur.^p. 213. 



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