1852.] SEDGWICK ON THE LOWER PALAEOZOIC ROCKS. 151 



group (No. 4) belongs, palseontologically, more to the Cambrian than 

 to the Silurian series. 



Before I left the Principality in 1832, 1 made some hasty traverses 

 through the lower palseozoic rocks of South Wales, between the " Si- 

 lurian System" and the coast of Cardiganshire. In each traverse 

 I met with the same kind of perplexing undulations, — slate-rocks, 

 flagstones, grits, sandstones, and conglomerates repeated again and 

 agaia. As a general rule, the conglomerates seemed most largely 

 developed near the western limits of the several sections, where the 

 higher mountain-ridges ended, and lower ridges of rocks, afterwards 

 called Silurian, began; and, as another general rule, the rocks 

 forming the immediate outskirts of the mountain-ridges dipped 

 towards the interior, so as not (at least in appearance) to pass under 

 these Silurian rocks. 



What then was the age of this undulating system of Cardiganshire, 

 &c. ? It was superior to the great group of Cader Idris (No. 2, e. 

 of the tabular view). Many portions of it were superior to the Bala 

 limestone. This was proved to demonstration by the sections at the 

 south end of the Berwyn chain near Mallwyd. Hence the whole 

 system represented No. 3 and No. 4 of the present tabular view; 

 and, agreeably to a nomenclature I afterwards adopted, was a great 

 expanded development of the Vpijier Cambrian series*. 



I had two objects in making these rapid traverses through the older 

 rocks of South Wales ; viz. to make out so much of the general 

 structure of the country, as to learn how I might best attack it during 

 the following summer ; and especially to find the prolongation of the 

 Bala limestone or its equivalents. Another summer came, during all 

 the early months of which I was crippled and unable to wield ahammer y 

 and, as for the Bala limestone, I neither found it, nor could I ever 

 make out with any certainty what was its exact representative among 

 the undulating masses of South Wales. As to the groups afterwards 

 called the Llandeilo flags, and the other beds afterwards coloured 

 Silurian in the ' Silurian System,' it formed no part of my task, nor 

 had I any time to study their relations. I knew that the author of 

 the * Silurian System ' had placed them over the great undulating 

 slate-rocks of South Wales ; and in two places, where I gave them in 

 1832 a passing look, I saw them apparently dipping under undoubted 

 newer groups, now known as Upper Silurian. 



My object in this retrospect is to show, that before I studied a 

 single section under the guidance of the author of the * Silurian 

 System,' and long before I had exchanged a word of amicable con- 

 troversy with him, my conception of the relations of the great Cam- 



* In formerly using the terms " Upper Cambrian System" and " Lower Cambrian 

 System," I neither asserted nor behevedthat the two series were capable of being 

 separated by distinct groups of fossils. All the evidence I had before rae rather 

 tended to an opposite conclusion. The terms seemed, however, convenient, as 

 giving us a good physical subdivision of a great complicated series of deposits, 

 and, at the time 1 first adopted them, were perfectly in agreement with the lan- 

 guage current among geologists, — simply designating a series of groups considered, 

 as a matter of convenient arrangement, apart from the rest of the groups in a general 

 section. 



