30 W. A. E. Ussher — Historical Geology of Cornwall. 



Whether the size of the boulders be exaggerated or not, it is 

 evident that the disturbance described was sufficiently powerful 

 to shift large stones from the existing beach to a point about the 

 average height of the Cornish raised beaches above high-water 

 mark, even allowing for an exaggeration of five feet in the height 

 to which the large boulder was said to be moved. At Polkerris, 

 near the Par estuary, " Raised Beach " has been engraved on the 

 map, apparently on the strength of the occurrence of isolated quartz 

 pebbles amid sandy debris on a small promontory some twenty feet 

 above the adjacent beach, which is composed of exactly similar quartz 

 pebbles. This phenomenon is much more likely to have been 

 produced by exceptional gales, or such disturbances as have been 

 described, than to be the relics of a raised beach, the lighter 

 materials of which had been dissipated by spray and rain, for the 

 raised beaches are usually too much consolidated to allow of such 

 facile dissipation. 



In February, 1759, Mr. Edmonds records a slight shock felt 

 at Liskeard for fifteen minutes, accompanied by blood-red rays. 



In March, 1761, on the day of the second earthquake at Lisbon, 

 the sea advanced and retreated five times four hours and a quarter 

 after ebb-tide, at five p.m., in Mounts Bay, rising six feet at 

 Penzance and Newlyn, and four feet at St. Michael's Mount. At 

 the Scilly Isles the agitation continued for more than two hours. 



In July, 1761, fluxes and refluxes occurred in Mounts Bay, and 

 at Falmouth, Fowey, and Plymouth. 



In 1789 fluxes and refluxes of the sea were observed at Penzance 

 and St. Michael's Mount. Earth shocks were felt on December 

 30th, 1832. 



In 1836 a slight disturbance of the earth was felt in the parishes 

 of Budock and Stithians. 



On October 20th, 1837, a slight shock is said to have been felt in 

 the Scilly Isles. 



On February 17th, 1842, an earthquake was felt between the 

 hours of eight and nine a.m., from Manaccan on the south to St. 

 Cubert on the north, a distance of twenty-five miles ; and from 

 Falmouth on the east to St. Hilary on the west, a distance of 

 eighteen miles. 



On July 5th, 1843, the sea was much agitated within Porthleven 

 Harbour. Three hundred yards from the north shore of the harbour 

 nothing unusual was observed. At one p.m. the sea rushed in 

 for fifty yards, reaching a height of four or five feet at Marazion. 

 At Penzance an agitation accompanied by strange currents was 

 observed. 



The effects of the disturbances above cited are eminently tran- 

 sient, except in abnormal shifting of detritus to higher levels, but 

 when we find that within the short space of a century Cornwall 

 has felt the spent force of earthquakes propagated from distant 

 centres of internal or eruptive motion, the probability of similar 

 disturbances emanating from much nearer sources, and productive of 

 considerable if not permanent effects, is at once suggested. Whilst 



