44 J. PRESTWICH ON THE QUATERNARY PHENOMENA 



reddish quartzite derived from the Budleigh-Salterton conglomerates 

 of the New Red Sandstone ; while small pebbles of red porphyries 

 from the Heavitree and Dawlish conglomerates are not rare, and 

 with them are a few pebbles of slate, and micaceous sandstone, 

 possibly from Devonian strata, and one large subangular pebble 

 of a reddish granite, perhaps from Cornwall. With the exception of 

 the few angular fragments of flint and the granite pebble, all the 

 above are well-rolled pebbles, such as might be formed on any 

 exposed shore. The only circumstance indicating ice- action is the 

 presence of the two large subangular blocks of sandstone, not of local 

 origin*, in the eastern section of the beach, and the granite pebble 

 in the western. It is evident that the drift of the shingle was then 

 from the westward and Devonshire coast, and that it was carried to 

 and round the then small Portland headland f. 



The list of shells from this beach includes many species not before 

 found in any raised beach ; but notwithstanding this the list falls 

 very short of the number of species now found on the Dorsetshire 

 coast. In the raised beach there are 28 species, whereas Mr. 

 Damon gives from this coast a list of 240, of which he informs me 

 that about 40 belong to the littoral zone. 



With one exception, all the shells are, according to my friend Mr. 

 Jeffreys, of species now living in the British Channel; but I would point 

 out that they are also all species which have a wide northern range 

 — that the Cyamium minutuin was first found in Greenland, where it 

 abounds — and that there is a marked absence of more southern forms. 



The mass of loam and angular debris overlying the Raised Beach is 

 not only newer than the beach, but is also subsequent to the anti- 

 clinal which raised the north end of Portland ; for at the foot of 

 the present high escarpment originating in that elevation, is a still 

 larger accumulation of this debris. Whether or not this deposit is 

 newer than the other drift-beds with which the raised and denuded 

 Weymouth area is dotted, there is here no direct evidence to prove ; 

 but I take it next in order, in consequence of its connexion with 

 Portland and with the Raised Beach. 



Similar deposits overlying other raised beaches have often been de- 

 scribed, and have generally been considered to be a " head " or talus 

 of subaerial origin. Mr. Godwin- Austen J, who has very carefully 

 examined into their structure, range, and origin, both on the English 



* If not transported by coast-ice, they may have been driven down by the 

 stream or floated by river-ice. 



t It follows from this that it is not necessary to assign a directly distant origin 

 to any of the pebbles of the Chesil Bank, as those from the Devonshire strata are 

 due rather to a transport which took place during the Quaternary period, when 

 the land between the distant headlands on which raised beaches have been found, 

 such as Berry Head, Start Point, Hope's Nose, and Portland, had not been in- 

 dented by the deep bay now sweeping round by Sidmouth, Lyme Eegis, and 

 Bridport. No doubt the coast-line at that period took a straighter course 

 from Hope's Nose to the Bill of Portland. This, however, is a subject which I 

 purpose to discuss elsewhere (lust. Civ. Eng.), as it bears upon questions connected 

 with the present set of the currents and tides, and on the origin of the Fleet. 



X " On the Superficial Accumulations of the coasts of the English Channel, 

 and the changes they indicate," Quart. Journ. Geol. Soc. vol. vii. p. 118, 1851. 



