ON THE GEOLOGICAL AGE OF CENTEAL AND WEST COENWALL, 



By J. H. COLLINS, F.G.S., MemUr. 



CONTENTS. 



Introduction. 



The Geological Age of tlie District an open question. 

 Ladock Beds. (Lower Devonian). 



Difficulties of Observation in Cornwall. 



Advantages afforded by Coast Sections. 



Extension of tlie Ladock Beds. 



Their Mineral Character. 



Their Thickness. 



Absence of Limestones. 



Absence of Fossils. 



Unconformability with Underlying Eocks. 

 Foivey Beds. (Upper Silurian ?) 



The Fish-beds. 



The Organic Eemains Generally. 



Extension of the Beds. 



Their Thickness. 



Their Mineral Character. 



Earity of Limestones. 



Unconformability with the Ladock Beds. 

 Lower Silurians. 



The Conglomerates. 



The Fossiliferous Quartzites. 



Fossiliferous Limestones. 



An Altered Coral Eeef. 



Pseudo-greenstones. 



Hornblende-schists and Serpentine. 



Great Extension of the Lower Silurians. 



Their Crumplings. 



Unconformability with the Ponsanooth Beds. 

 Ponsanooth Beds. (Cambrian ?) 



Their Existence not Previously Suspected. 



Their Extension and Thickness. 



Pseudo-greenstones. 



Gneiss and Knoten-schiefer (spotted killas). 

 Intrusive Roclcs. 



Pre- granitic Intrusions (greenstones and mica-trap.) 



Granitic Intrusions (granitic bosses). 



Post-gi-anitic Intrusions (el vans). 



