37 



PART II. 



A CLASSIFICATION OF THE PLEISTOCENE 

 DEPOSITS OF CORNWALL. 



OLDEST DEPOSITS. 



The existence of a quartz gravel in a district composed of Diallage 

 and Serpentine on Crousa Down, and the occurrence of a similar 

 gravel resting on granite in Crowan, both patches being not only 

 disconnected with the pi-esent drainage system, but situated at such 

 altitudes as to preclude the idea of transport from adjacent sources, 

 lead one to infer : 



1st. That (a) they were formed from the degradation of the Killas 

 and its associated quartz veins ; or (fe) from the disintegra- 

 tion and transport of a quartz conglomerate rock. 



2nd. That they are the relics of deposits originally much more 

 extensive, formed at a time when the country possessed an 

 entirely different configuration.' 



There being no means of arriving at a definite conclusion as to 

 the age of these gravels, or of the sands and clays of St. Agnes 

 Beacon, I can only include them within a long period ranging from 

 Cretaceous to early Pleistocene times, at the same time inclining to 

 the belief that the quartz gravels are either of Tertiary age or a 

 re-assortment of Tertiary gravels. 



This indefinite chronology is not to be wondered at, when we 

 reflect on the absence of evidence respecting the extension of Creta- 

 ceous and Tertiary deposits to the westward of Haldon ; and specu- 

 late, in the event of such extension of either formation having 

 taken place, on the influence local sources of supply would have had 

 on the marginal sediments there thrown down. 



1 This is also Mr. Tyack's opinion. 



