J. B. Hill — The Paiceozoics of West Cornwall. 207 



recent survey, neither invalidates the map published by De la Beche 

 •nor the subsequent conclusions of Murcliison. It has, on the other 

 hand, not only brought their generalizations within more definite 

 limits, but has carried the investigation a step farther by demon- 

 strating the relations between the older and newer Palaeozoics of 

 Cornwall. 



As the lithological characters, the structural features, and the 

 mutual relations of the divisions into which the killas has been 

 differentiated have already been the subject of former communica- 

 tions, both to the Koyal Geological Society of Cornwall^ and to 

 the Summaries of Progress of the Geological Survey,- they will only 

 be treated briefly in this paper. They will, moreover, be fully 

 described in the Survey memoirs, but, as the results of recent 

 investigations constitute an important advance in the elucidation of 

 the geology of the West of England, it will be convenient to present 

 a,t once an outline of these conclusions, as the official publications 

 will not be immediately forthcoming. 



The main object of this paper is to demonstrate the existence of 

 an important unconformity dividing the Upper and Lower Paleeozoic 

 formations of West Cornwall. Evidence will also be submitted 

 pointing to the natural sequence of the four divisions of the Lower 

 Palceozoics, and to the Lower Devonian age of the conglomeratic 

 «eries of Manaccan and Grampound. 



LitTiology of the Lower Paleozoic divisions. 



The lithological characteristics of the divisions will now be briefly 

 touched upon. 



Veryan Series. — This group consists of blue and grey slate with 

 sandy alternations, thin dark limestones, and dark-coloured cherts. 

 Notwithstanding the occurrence of chert and limestones the sandy 

 interlaminations are frequently coarse, but being largely composed 

 of soft grains are readily cleaved. This series, which also includes 

 the Carne quartzite, is further characterized by the presence of 

 manganese, which stains the slate. 



Portscatho Series. — These consist of blue and grey clay slates, 

 alternating with harder beds showing every gradation from a sandy 

 slate to a fairly strong grit. The latter are characterized by the 

 predominance of quartz and the comparative abundance of clastic 

 mica. The marked feature, however, which distinguishes them 

 from the Veryan Series is the absence of limestone, except at their 

 mutual junctions. This dearth of calcareous material also applies 

 to the Falmouth and Mylor divisions. 



Falmouth Series. — This series consists of argillaceous and fine 

 sandy alternations, varying in colour from green to grey and buff, 

 although blue argillaceous beds sometimes appear. The contrasting 

 tints produce a variegated appearance common to this group. Their 

 mode of decomposition is equally characteristic. The sandy seams 

 become readily friable, are unctuous to the touch, and weather into 



' See paper already cited. 

 2 From 1897 onwards. 



