50 



CORNISH POST-TERTIARY GEOLOGY. 



12. Sea Beaches, RiverGravels, 

 Alluvia and Peat Growth. 



11. Blown Sands. 



10. Eiver deposits ■with estud- 

 rine sediments intercalated in 

 some Stream-tin Sections 

 near the coast, also Peat 

 beds. River deposits with 

 occasional Peat beds inter- 

 calated in Inland districts. 



9. Planed Eock reefs, Gravel 

 and Sand Bars. 



8. Marine and estiiarine de- 

 posits in some Stream-tin 

 Sections. River Gravels and 

 Alluvia in inland districts. 



7. Submerged Forests and 

 Forest Bed in some Stream- 

 tin sections. 



The presence of man in- 

 dicated, with remains of 

 deer (including the Irish elk) 

 and oxen. 



5. Head in inland districts 

 and on the cliffs. River 

 Gravels. Stream- tin Gravels. 



5. Probably River Gravels, 

 as in Devon, connected with 

 the present drainage system. 



4. Raised Beaches and Old 

 Blown Sands. 



Erratic boulder at Saun- 

 ton (North Devon). 



TABLE OF CLASSIFICATION. 



PHYSICAL CHANGES INDICATED. 



Gradual overspread of Blown Sands on parts 

 of the North-western coast of Cornwall, en- 

 tombing hamlets and churches. 



Local stoppages or diversions of drainage 

 giving rise to peat growth and morasses in 

 valley bottoms. Climate of the Central and 

 Western parts of Cornwall only favourable tor 

 the growth of underwood. 



3. Boulder Gravels. 



2. Deposits not recognizable. 

 Debris swept to lower levels 

 beyond the existing coast- 

 line. 



1. Gravels of Crousa Down 

 and Crowan ; Sands and 

 Clays of St. Agnes. 



Possible oscillation in the subsiding move- 

 ment, not yet counteracted. 



Advance of the sea to its old cliff bounds ; 

 destruction and entombment of the marshy 

 forest lands fringing the coasts; decay of 

 forests in inland districts through the preva- 

 lence of unfavourable conditions. 



Continuance of subsidence, gradually circum- 

 scribing the forest plains, but allowing sudden 

 encroachments of the sea from time to time 

 as the successive terraces in -its old plain were 

 surmounted. 



Climate ameliorating and becoming suitable 

 for the growth of Oak, Alder, Hazel, etc.. on 

 a large area beyond the limits of the present 

 coast-line. 



Elevation, perhaps culminating in conti- 

 nental conditions. Seasons becoming more 

 marked. Considerable snow-fall and penetrat- 

 ing frosts. Much surface water. Cold di- 

 minishing. Subsidence. Rainfall greater than 

 now. 



Land rising. 



Culmination of subsidence at an average of 15 

 feet below the present level : Wales, etc., being 

 submerged, in places, to a depth of 1500 feet. 



Stranding of occasional icebergs or floes 

 drifted from Ireland, Lundy Island or the 

 Northern counties. 



Land subsiding. Liberation of much surface 

 water with torrential power by melting of 

 snows during intermittent warm periods and 

 the succeeding amelioration. 



Land at considerable altitude, possibly conti- 

 nental Approach of cold : great quantities of 

 .snow accumulating on the highlands (possibly 

 giving rise to a local glacier system). 



Old surface configuration prior to the initia- 

 tion of the present lines of drainage. 



