and the Palceozoic System of England. 315 



Now if the groups 2, 3, 4, 5, &c. be unbroken and con- 

 tinuous, we can only account for the position of the Cambrian 

 group (No. 1) by the hypothesis of a great fault ; and in this 

 way, and this way only, can we bring the beds (No, 1) into co- 

 ordination with their supposed place in the ideal vertical section 

 (fig. 5). 



As a matter of fact, however, there is no necessity for the in- 

 tervention of a great fault, nor does any such fault exist*. The 

 groups 2, 3, 4, &c. are not the parts of an unbroken sequence ; 

 but here (as in the vertical section, fig. 2) the Wenlock shales 

 (No. 4) are, by a great overlap, brought into contact with the 

 Llandeilo groups ; and, to make the ideal vertical section (fig. 5) 

 correct, we must remove the great Cambrian group (No. 1) from 

 its place, and interpolate it below the Wenlock group (No. 4). 

 In short, the relations of the older groups in the Llandeilo 

 country have been completely misinterpreted in the ^ Silurian 

 System.'' 



It follows, from what has now been stated, that the sec- 

 tions, both of Caer Caradoc and Llandeilo, are broken and dis- 

 continuous sections, and that they cannot, therefore, be used 

 correctly as typical sections for the establishment of a true geo- 

 graphical nomenclature. And I may here remark, that nearly 

 all the mistakes of classification and controversies of nomen- 

 clature, respecting the older fossil-bearing groups of Wales, 

 have arisen from an inattention to the fact, that all the upper 

 groups, commencing with the May Hill sandstone, are, com- 

 monly, either unconformable to the Cambrian series, or, by 

 some deceptive overlap, are brought into an abnormal super- 

 position, which interferes with, and absolutely vitiates, their 

 relations to the older beds on which they rest. It has con- 

 stantly been assumed (sometimes very erroneously) that any 

 shelly sandstone immediately under the Wenlock shale must be 

 considered as a Caradoc sandstone; and this assumption ine- 

 vitably led to another, viz. that a large group of rocks existed 

 below the Wenlock shale (both in Cambria and Siluria), which 

 contained characteristic groups of Cambrian and Silurian fossils 

 inseparably united. From these two assumptions, followed a 

 third — that all the fossiliferous rocks, from the highest Silurian 

 to the lowest Cambrian, formed but one palseontological system. 



* It may be perhaps contended that the author of the " Silurian System' 

 does not, in his sections of the Towy, indicate the place of any great fault. 

 But how are we to put the Llandeilo groups over the rocks which are co- 

 loured Cambrian without the supposition of a great upcast at the northern 

 end of the sections ? It is absolutely impossible to explain the sections of 

 the Silurian System, pi. 34, fig. 9 (for example), without the intervention 

 of a fault. 



