24 THE GEOLOGICAIi AGE OP CENTRAL AND WEST CORNWALL. 



resembling strata of a higher antiquity, hereafter to be referred 

 to. The figure shows its mode of occurrence at the Nare Point. 



It would be difficult to estimate the thickness of the LadockBeds 

 with any approach to accuracy, without devoting a much larger 

 amount of time to their examination than I have been able to 

 give, but the Ladock Valley Section seems to show that they are 

 not more than from 1000 to 1500 feet thick in all. 



The Ladock Beds do not appear to include any limestones 

 whatever, and it is doubtful whether they contain a single fossil 

 of any kind, following the Survey Maps, I formerly regarded 

 the thin black limestones and associated beds of the Van, near 

 St. Austell, and of the Towan Head at Newquay, as of the same 

 age as the Ladock Beds, but I now believe them to underlie 

 these. 



" Only two inland localities have been reported as fossiliferous 

 within the area covered by these beds, viz : — at Poltisko near 

 Truro, where Mr. Peach found " part of the stem of an encrinite 

 many years ago" f Trans. Roy. Geol. Soc. Corn., VI, I8iy, and at 

 Wheal Hope, in Perranzabuloe, from which locality Mr. W. 

 Mansell Tweedy believed he obtained some encrinital stems 

 also many years ago fRep. Roy. Inst. Corn). These localities, 

 and many others, have been patiently searched by Mr. Clark and 

 myself, but hitherto, we have found nothing of undoubted organic 

 character ; indeed the obscure markings which we have found 

 appear to us to have more of a mineral than an organic origin. 

 In the sandstones, however, we have found certain ferruginous 

 nodules occurring in lines corresponding with the bedding, and 

 these contain from a mere trace up to about one per cent, of phos- 

 phoric acid, which may, perhaps, be derived from an organic 

 source. I have not, however, been able to detect organic structure 

 in any of them.'^' 



The absence of fossils of all kinds over so considerable an 

 area composed of sedimentary rocks, is certainly a remarkable 

 fact, and it leaves us still somewhat in the dark as to their 

 geological age. All that can be said with certainty is that they 

 were laid down after the consolidation, contortion, and denudation 

 of the Lower Silurian rocks, and, as I believe, the rocks next to 



* Collins, Preliminary Note on the Stratigraphy of West Cornwall, Trans. 

 Boy. Geol. Soc. Corn. X, 1, 1878, 



