206 mr. e. a. martin on [May 1909, 



12. Some Recent Observations on the Brighton Cliff-Formation. 

 By Edward Alfred Martin, F.G.S. (Read February 10th, 

 1909.) 



[Abstract.] 



The Author records in his paper certain features presented by the 

 face of the cliffs between successive falls at Black Rock, Brighton, 

 during the past eighteen years. As the cliffs have worn back, the 

 base-platform of Chalk grows in height, and the layer of sand 

 which Prestwich found above the Chalk grew thinner and thinner 

 until finally it completely disappeared. At the same time, the 

 raised beach has grown in thickness from 1| to 12 feet. In 1890 

 there were 6 feet of sand, with a foot and a half of beach above it. 

 There was practically no protection at this date in the shape of 

 groynes. In 1892 the sand had decreased to betAveen 3 and 4 feet, 

 but the beach remained as in 1890. Many falls of cliff took place 

 between 1892 and 1895, and at the latter date the beach had 

 increased to between 4 and 5 feet. The eastern limit of the beds 

 had become more clearly defined, the trough in the Chalk in which 

 they had been defined taking an upward direction about 300 yards 

 east of the Abergavenny Inn. Many blocks of red sandstone had 

 become dislodged, and were lying on the modern beach. In 1897, 

 10 feet of chalk formed the lower portion of the cliff, with 8 feet 

 of raised beach above it in places, but there was a mere trace 

 of sand left. The rubble-drift above was seen to be distinctly 

 stratified. Many masses of red sandstone had fallen out of the cliff, 

 the largest measuring 5 feet in its greatest dimension. In 1899, 

 the raised beach had reached a thickness of 10 feet. Great masses 

 of moved and reconstructed chalk were observed on the eastern 

 boundary embedded in the beach. Two rounded lumps of granite 

 were extracted from the beach. In 1903, the beach was but a 

 little over 8 feet thick in the exposed parts, but the platform of 

 Chalk was 14 feet thick. The upper portions of the beach, which 

 were the least consolidated, had fallen away in such a manner as to 

 leave cave-like gaps beneath the rubble. The number of red sand- 

 stone blocks which lay on the modern beach was remarkable, forty 

 such blocks being counted in a space of 50 yards square. In 1906, 

 the raised beach had increased from 15 to 20 feet : farther west, 

 however, the thickness was not so great. In 1908, there were 

 17 feet of Chalk, 12 feet of beach. It is noteworthy that, as the 

 degradation of the cliff proceeds, the material is rapidly carried 

 away by the sea. No talus remains for any length of time, and 

 if the material is to be prevented from disappearing into deep water, 

 some such contrivance as chain-cable groynes seems to be demanded, 

 fixed somewhere between low and high tide-marks. The only 

 organic remains observed in the cliffs were some fragments of shells, 

 found at the top of the raised beach. 



