THE MENDIPS : A GEOLOGICAL REVERIE. 



253 



they only attain a thickness of 200 or 300 fcot in the Bristol* 

 or Mondip area. And this I take to be evidence of the fact 

 that this area was not submerged till near the close of 

 Triassic times. 



Then came the irruption of the sea. At first only a few 

 bivalves found their way into our area. The bone bed at 

 the base of the Penarth series does indeed include a great 

 number of tooth, bones, and scales of fishes and other verte- 

 brates including the tooth of the Coratodus, a fish closely 

 allied to tho Flathead of Queensland waters. But these wore 

 the unfortunates who succumbed to tho changed conditions 

 of environment. The immigrants who made their home in 

 the lake, which was now in connection with the southern 

 Rhoetic Sea, were restricted to a few bivalves. They were 

 soon followed, however, by the teeming wealth of Liassic 

 times, and the abundan t fauna of the succeeding Oolites. 



Those who are accpainted with the Lias only in its typical 

 development, at Lyme Regis or Whitby, for example, might 

 well be puzzled at first sight of the Lias on Mondip. It is 

 here a thin and meagre shore deposit, with none of the 

 characteristic Ammonites so familiar to collectors. In some 

 places, as at Shepton Mallet, the Lias rests directly on the 

 worn and upturned edges of the Palaeozoic rocks, and con- 

 sists of a close, white limestone ; in others, as at Harptree 

 and Emborrow, it has been converted into a silicious chert. 

 ELsowhoro, as at Holwell, Rluetic and Liassic remains have 

 been found in so-called dykes, which must have been fissures 

 at tho time when the shallow waters of the Mesozoic soa 

 played over the margin of Mendip Isle. At what exact period 

 the fissures were thus filled in it is difficult to say. Most 



* There would Bocm to be a local uneonformability in the Trias dis- 

 played in tho new G. W. 11. cutting near Brislington. 



