270 THE GEOLOGICAL STRUCTUEE OF SOITTH CORlSrWALL. 



Lithologieally these Caradoc beds are characterized by a 

 series of quartzites, conglomerates, and limestones. Their 

 strike at G-errans Bay, if prolonged, although curving round a 

 little to the west, undoubtedly becomes correlated with precisely 

 similar beds occurring south of the Helford river at the Naro 

 Point, and also containing the same organic remains which mark 

 their north-eastward extension, and also underlaid by the same 

 slaty beds. 



On the present survey maps these Lower Silurian rocks, 

 although containing the same fossils and having the same min- 

 eral characteristics and occupying the same geological horizon 

 as those at Gerrans Bay are nevertheless coloured as Devonian. 



"We find that these Caradoc beds are everywhere underlaid 

 by the still lower series of strata to which we have already 

 alluded, and which I have no hesitation in calling the Llandeilo, 

 the member which immediately underlies the Caradoc. These 

 Llandeilo beds consist of a great series of slates and impure 

 thinly bedded sandstones, the whole being characterized by the 

 immense thickness of dark carbonaceous looking slates, which 

 is quite the character of this division of the system in other 

 localities, as in Wales, and also in Scotland, 



.The lowest of these Llandeilo beds (the Cambrian of Mr. 

 Collins), are well exposed in the neighbourhood of Penryn, 

 where they abut against the granite, and from this point to the 

 Caradoc of Veryan Bay and the Nare Point, there is a gradual 

 ascending section, so that a line passing from the granite of 

 Penryn through Palmouth to the "Old Wall Buoy," would 

 pretty nearly indicate the thickness of the Llandeilo and Caradoc 

 divisions in this region, which will, I think, be something like 

 10,000 feet. From the Llandeilo rocks no fossils have as yet 

 been recorded. It would almost seem as if every organism 

 originally contained in the strata had been destroyed by the 

 metamorphism that the beds had undergone during the forma- 

 tion of the granite. At the same time, however, it is highly 

 interesting to note the fact that the dark carbonaceous slates are 

 such as would result from the graptolites which are so highly 

 characteristic of this division of the Lower Silurian, and that 

 such also is the aspect of the rocks which make up this member 

 of the system both in Wales and in Scotland ; consequently I 



