264 JURASSIC. 



many Belemnites. The platform of Belemnite-stone, which may well be seen at 

 the base of Golden Cap, at low-tide, and the marls immediately beneath it, yield 

 a profusion of Belemnites, including B. loigissimus, B. clavahis, B. pollcx, and 

 B. Biicklandi (with sometimes the ink-bag preserved in the anterior of the 

 phragmacone).^ The Belemnite Beds extend from Black Ven through the cliffs 

 east of Charmouth, to the base of Golden Cap, and are not exposed east of Seatown. 

 Above them come the Green Ammonite-beds, bluish-grey clays with small nodules 

 of limestone, about 100 feet in thickness. These beds are so termed by collectors 

 from the green tint of the calc-spar which fills the chambers of the characteristic 

 Ammonite, A. latcEcosta. Fragments of this fossil are extremely abundant, and 

 perfect specimens, as a rule, are only obtained from the small cement-stones. In 

 Dr. Wright's opinion this species may be the middle age condition of A. Henleyi; 

 but, as Dr. Oppel suggested, it appears to represent A. capricormis? Other species 

 found in these beds are A. Henleyi, A. Bechei, A. Loscombi, A. fiinbyiatiis. and 

 A. Davai : the last-named species being taken by Dr. Oppel to indicate the 

 zone. 



The Three Tiers are prominent bands of fissile, micaceous, and calcareous sand- 

 stone, well seen in Golden Cap ; they are, as a rule, unfossiliferous. They occupy 

 a thickness of from 30 to 40 feet, and mark the base of the Middle Lias (zone of 

 A nimo lilies niargaritatus) . 



In Somersetshire the thickness of the Lower Lias varies from 

 a few feet, in the neighbourhood of the Mendip Hills, to about 

 300 feet. Good sections of the lower beds of limestone are ex- 

 posed on the coast at Watchet, and eastwards at intervals to Kilve. 

 The beds are very much faulted. The zones oi Ammonites plaiiorbis, 

 A. Bucklandi, and A. Tiirncri may be observed, but fossils are not 

 numerous, except in particular layers. Near Watchet, specimens 

 of A. Joh7istoni [torus), a ribbed variety of A. planorbis, are not 

 uncommon, and as the mother-of-pearl layer of the shell is well 

 preserved, the fossils glisten with iridescent colours on the loose 

 blocks of stone, or on the pavements of rock on the foreshore. 



At Selworthy, near Porlock, the Lower Lias and Rhsetic Beds 

 are probably faulted against the Devonian rocks, as they dip at a 

 high angle towards them. 



The Lower Lias in the Vale of Ilchester consists of three 

 members : — 



3. Blue and brown clay (worked for brick-making). 



2. Even-bedded blue limestones and shales ; largely quarried at Keinton 



Mandefield, King Weston, Somerton, and Queen Camel. 

 I. Rubbly white earthy limestones and marls, with Ostj-ea Liassica and 



Modiola minima ; resting on the White Lias (Rhastic). 



The uppermost division (3) occurs over the flat country bordering 

 the Middle Lias escarpment, north of Martock, at Marston Magna 

 and East and West Lydford. 



In the neighbourhood of Wedmore, at Street, and along the 

 Polden Hills, the lower beds of the Lias consist of comparatively 

 soft argillaceous limestones, sometimes graduating into a marl, 

 together with coarse and compact blue limestones (termed 'clog'). 



1 Phillips, Monograph on Belemnites ( Pal neon tograph. Soc.) ; Day, Q. J. xix. 

 278 ; Bristow, Horizontal Sections, Sheet 21 (Geol. Survey). Drawings have 

 been made from the 'Fossil Sepia' obtained from the Dorsetshire coast. 



* Die Juraformation, pp. 155, 157. 



