168 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 6, 



nic remains distinct from those 1 had called " Lower Silurian." 

 Improving in the following years the description of the Silurian re- 

 gion, and having completed as well as I could by my own labours 

 (aided by a few kind friends resident in the country) the collection 

 of its typical fossils, 1 published in 1839 the " Silurian System," as 

 founded on my own researches. This work was accompanied by a 

 map, which as far as the parts coloured Silurian are concerned, has, 

 I believe, been found little fault with ; the distinctions of the Upper 

 and Lower Silurian rocks with their subordinate formations (all 

 perfectly conformable, be it observed, to each other) being ac- 

 curately laid down in reference to other overlying deposits. But 

 notwithstanding the labour bestowed upon it, this map was neces- 

 sarily very defective in the boundary-line between the typified Lower 

 Silurian and the untyplfied Cambrian rocks. In the northern part 

 of the map that line was, indeed, for the most part inserted, at my 

 request, by Professor Sedgwick himself*; and in Central and South 

 Wales it indicated, according to my view, little more than that to 

 the west of it, the so-called Cambrian rocks were then neither zoolo- 

 gically nor physically explored — a task which, as repeatedly an- 

 nounced to the Geological Society and expressly declared in my 

 work, was left exclusively to Professor Sedgwick. But although it 

 was, so to speak, a point of honour with me not to trench upon the 

 privileges of the eminent geologist who had engaged to describe the 

 Cambrian region, I can truly say, that I repeatedly urged him to 

 determine the organic remains of those slaty rocks ; for I then 

 thought, I repeat, that they would be found to be in that manner 

 essentially distinguished from my Silurian types. Years however 

 rolled on and this desirable end was not accomplished ; and no pe- 

 culiar fossils having to this day been published, the Cambrian sy- 

 stem consequently remained without organic characters of its own. 

 It was, in fact, a great physical mass without the vitality of a 

 system. 



All that I knew of the fossils of the so-called Cambrian rocks, at 

 the period of the publication of my work, was, that the chief forms 

 which occurred in their Eastern or upper division, as at Bala, were 

 specifically the same as my Lower Silurian types, — a strong proof 

 that there was a gradual transition from the one to the other, and that 

 the boundary-line drawn upon my map between the tracts named 

 Siluria and Cambria was merely provisional, and had been laid down 

 on no fixed geological principle. Thus in speaking of some of these 

 Bala fossils my words were — "As these shells abound also in the 

 Lower Silurian rocks, it would seem that as yet no defined line of 

 zoological division occurs between the Lower Silurian and Upper 

 Cambrian group ; and that as our knowledge extends, we may pro- 

 bably Jix the lowest limit of the Silurian beneath the line of demarca- 

 tion which has for the present been assumed f." Surely words could 

 not more explicitly show, both that the boundary-line marked in the 

 map was not a natural limit, but simply a geographical (not a true 



* See description of the map, Sil. Svst. p. xxix. 

 t Sil. Syst. vol. i. p. 308, 



