166 W. A. E. Ussher — Post- Tertiary Geology of Cornwall. 



V. — Post-Tertiary Geology op Cornwall. 1 



By W. A. E. Ussher, F.G.S. 



Part III. — The Eaised Beaches and Associated Deposits of 

 the Cornish Coast. 



THE following observations of the Cornish Cliffs are given in 

 order, proceeding round the coast from Plymouth. The num- 

 bers and letters have been prefixed to facilitate subsequent reference. 



1. Mount Edgecombe, near Plymouth. 



a. De la Beche (Geological Manual, p. 159) mentions the occur- 

 rence of rolled shingles, covered by fragments of slate and red 

 sandstone near Eedding Point ; the height of the deposit is not given. 



b. Near Mount Edgecumbe Obelisk I noticed brown and reddish 

 coarse-grained sand filling an inequality in the limestone at about 

 30 feet above the river ; this is probably a trace of contemporaneous 

 deposition with the Hoe Eaised Beach. 



2. Looe Island. Mr. Pengelly (Trans. E. G. S. Corn. vol. vii. p. 

 118) noticed the occurrence of layers of comminuted, and somewhat 

 rounded, yellowish matter containing rather large rounded slate 

 fragments and ordinary pebbles, on the northern cliffs of the island. 

 Height above high water not given. 



3. St. Austell's Bay. 



a. A point at which Eaised Beach is engraved on the map, at Pol- 

 kerris, is capped by 8 feet of Head of small angular killas fragments, 

 occasional quartz pebbles were found, being either the relics of a 

 raised beach, or hurled to a height of 30 feet above high-water 

 mark by storm waves from the beach below. This point is joined to 

 the main cliff by a very narrow ridge of rock. 



b. Near Pol mere the Head rests upon micaceous slates, and in 

 places presents a rudely stratified appearance. 



c. Near the Par Inn, a stratified gravel of subangular grit, quartz, 

 slate, and granite stones, and occasional boulders, 4 to 5 feet in 

 thickness, occurs at about 20 feet above high water. 



d. On the south side of Spit Point, fine gravel with pebbles of 

 quartz and boulders (one flint pebble found and a fragment of Car- 

 dium, ? in situ) 8 feet in thickness, and at base o feet above high 

 water, occurs on the low cliffs. 



e. Near the above the base of the raised beach is 10 feet above 

 high water, it consists of fine gravel alternating with greyish sand 

 upon large pebbles and unworn blocks of the subjacent rock. The 

 deposit is 10 feet in thickness, the layers appear to dip seaward. 



4. Gerran's Bay. 



a. On the eastward side of the beach the section consists of — 



Brown soil with angular stones 5ft. Oin. 



Brown loam with angular fragments of slate and quartz ... 10ft. Oin. 

 Beds of consolidated black sand and quartz gravel, lying 

 unevenly on the subjacent rock at about five feet above 

 high water 4ft. 6in. 



De la Beche (Eeport, p. 430) mentions the consolidation of portions 

 1 Continued from the March Number, p. 110. 



