THE GEOLOGICAL STBTJCTITBE OF SOUTH CORIfWALL. 271 



think we are justified in using the term Llandeilo for the beds 

 which immediately underlie the Caradoc. With reference to the 

 boundary between these two divisions, this is a task that has yet 

 to be accomplished, of course the dividing line must be less or 

 more an arbitrary one. I do not think that the colouring in the 

 present survey maps which separates the Lower Silurian from 

 the so-caUed Devonian (or as we think Llandeilo), indicates any 

 well marked bed or beds which would serve as a horizon, or line 

 of separation, which appears to be entirely a conjectural one. 



In the region to the south and south-west of Falmouth no 

 higher formation or group of strata than these we have already 

 described occur, viz., the Caradoc beds south of Helford river. 

 If, however, we draw a line from Falmouth in a north-east 

 direction towards Looe, following that line we get a continuous 

 ascent from older to newer formations, passing through what I 

 have termed the Llandeilo upwards to the Caradoc, through the 

 Lower and Middle Devonian, the Upper Silurian being altogether 

 absent. 



As far as I have been able from very limited observation 

 to make out the geological structure of the district, and the 

 order of succession of the various formations through which the 

 line already alluded to passes, I am inclined to think that the 

 Lower Devonian comes on in the neighbourhood of St. Austell, 

 or on the coast about the Pentewan valley, and from this point, 

 with the exception of a few reversals of dip, we continue 

 ascending up to the Middle Devonian of Looe, which brings us 

 close to the base of the Plymouth limestone group. 



Let me remark that the Fowey and Polperro beds, so replete 

 with organic remains, have hitherto by most observers been 

 regarded as of true Devonian age : I am not aware that any 

 geologist at the present day, besides Mr. Collins himself, has 

 attempted to identify them with the Upper Silurian. 



There is a point of great interest connected with these 

 Devonian rocks of Cornwall, and the organic remains which 

 they contain. In Devonshire and other counties of England, 

 where strata of this age occur, they as a rule contain only an 

 invertebrate marine fauna, such as corals, shells, &c., the 

 remains of fishes being entirely or nearly absent. In the old 

 red sandstone of Scotland, which is the equivalent of the 

 Devonian, this state of things is completely reversed. The 



