﻿Pig. 1. — Vertical section of the Llansatuel 

 Group, showing the relative positions of 

 the more important graptolites. 



Pengelli 



Shaees 



c,. 



v_ 



'C 2 zone or M. 

 f communis. 



Clynmarch 

 Grits 





- J— 





s^r=^rz=^=z 





^=Z=^H 



1 



=^S_=E^ 



o 

 o 



i 



1^55? 



1 



; — - — -- — - 



d 



.. 



o 

 o 

 N 



i-t 



H-zEFrrr 



■f 



ilBlBIl 



§ 



NO 



JEE—^ErlEr 



V 



^=S;X^=^S=r?" 





f^^7JEE^_ 



Monograptus marri. 



Monograptus exiguus, 

 M. cf. becki, M. 

 runcinatus. 



( M. gregarius, M. 

 | jaculum {?J, CI. 

 ■{ tornquisti, Glijpto. 

 I tamariscus, Meso- 

 { graptnsmagnusf!) 



( M. cyphus, M. 

 j revolutus, M. cf. 

 -{ atavus, CI. rectan- 

 j gularis,Cl.hughesi, 

 {& Cl. tornquisti. 



[Scale: 1 inch = 500 feet.] 



our best fossil horizons. 

 They may be placed at 

 the base of the zone of 

 Monograptus gregarius of 

 Prof. Lapworth, as they 

 contain Monograptids of 

 the cyphus type, in ad- 

 dition to Mesograptus 

 and Climacograptus. On 

 the north - west higher 

 zones appear, and the 

 upper beds roll con - 

 tinuously towards the 

 rising ground of the 

 watershed, and cover a 

 wide extent of country. 



To sum up, there are 

 in this district three 

 main groups, the mutual 

 relations of which are 

 beyond question. In the 

 highest the sequence of 

 the individual members 

 is clear from the strati- 

 graphy, and is confirmed 

 by the palaeontological 

 evidence ; in the second 

 the maximum develop - 

 ment of grits and con- 

 glomerates is certainly 

 below that of the mud- 

 stones and shales. 



The structure of the 

 district is, at first sight, 

 a simple one, owing to 

 the monotonous north- 

 westerly dip and north- 

 easterly strike ; but de- 

 tailed mapping brings 

 out unexpected compli- 

 cations in the distribu- 

 tion of the beds. 



North and west of 

 Llansawel the folding 

 is simple, and has a 

 Caledonian direction ; the 

 beds follow one another 

 regularly, except for a 

 certain amount of rolling 

 in the upper part of the 

 series, which causes a 

 continual change in the 



