OEOr.OGY OF TtlH AVON BASIN. 



13 



point in.irkod li on the map, Coal ]\ioasurcs, presumably 

 Pennant Sandstone, ai-o thi'own into juxtaposition with Old 

 Red Sandstone. Taking the dip of the beds (about 20° 

 S.S.R.) into consideration, the beds oC the Old Red Sand- 

 stone at this point are certainly not less than 700 feet from 

 the top of that series. Supposing that wo have here tho 

 lowermost beds of tho Pennant brought down to tho level 

 of tlieso Old Red beds, then wc have intermediate to tiiese 

 two — 



Lower Coal Measures . 



. 1500 foot 



Millstone Grit . 



. 500 „ 



Upper Limestone Shales 



. 500 „ 



Mountain Limoatono . 



. 1500 „ 



Lower Limestone Shales 



. 300 „ 



Old lied Sandstone 



. 700 ,, 



5000 „ 



It is possible, however, tliat tlic Millstone Grit is not 

 de\relo])ed here. It is said not to bo developed at Tieken- 

 ham, on the Nailsea side of the Clifton-Clevedon ridge, 

 and it is not mapped by the Survey or Mr. Sanders near 

 Clevedon, where we should expect it to occur. Striking 

 out this 500 feet, therefore, and striking out another 500 

 foet for not impossible thinning of some of tho other beds, 

 wo still have 4000 feet separating the beds to the W. of h 

 fi-om tho beds to tho lil. of that point. 



In another way tho magTiitudo of the displacement may 

 be seen and a rough estimate of its amount may be made, 

 riio Mountain Limestone being here thrown down far be- 

 neath tho surface of the ground, and the beds dipping to 

 the S.S.E., this rock should emerge to the N.N. W. And 

 m the Portishead-Clevedon ridge we see that it actually 

 does so. Now the emergence of the point of junction of tho 

 Lower Limestone Shales and the Old Red Sandstone is dis- 



