and the Palmzoic System of England. 313 



Fig. 4. A Section representing the relations of the groups of Caer 

 Caradoc to the overlying Siluriart rocks. 



Fig. 4. Fig. 5. 



Old red sandstone. 



^v5:^Li 



Ludlow groups. 



Wenlock limestone. 



Wenlock shale. 



Conglomerates, Nor- 



bury beds. 

 Sandstones, &c, (l\Iay 



Hill group). 



Shelly sandstone of 

 Horderley and Caer 

 Caradoc. 



Shales, &c. with Bala 

 and Llandeilo fossils. 



Old rock of the 

 Longmyud. 



Carboniferous, &c. 



Old red sandstone. 



Wenlock and Ludlow. 



Caradoc sandstone. 



Llandeilo flags. 



Cambrian. 



In the section fig. 4 (from the neighbourhood of Caer Caradoc), No. 4a 

 is, both from its position and fossils, separated from No. 3 and grouped 

 with No. 4 (Wenlock). In the * Silurian System ' Nos. (4a) and (3) were 

 erroneously placed in one group— the " Caradoc sandstone." The group 

 (4«) is here regarded as the true physical and palaeontological base of the 

 Silurian series. 



This vertical section (fig. 5) represents the supposed sequence of deposits 

 near Llandeilo as given in the 'Silurian System.' But it is erroneous; 

 as No. 1 ought, in a true vertical section, to be above No. 2. The origin 

 of this mistake is explained by help of the profile section, fig. 6, which 

 represents the general position of the groups near Llandeilo, without pre- 

 tending to give any of the intricate contortions. 



