34 



J. PRESTW1CH ON THE QUATERNARY PHENOMENA 



To these Prof. Rupert Jones has added PolystomeUa striatopunc- 

 tata, and a Cythere, sp. nov. (?), but related to some known forms. 



A curious feature in this old beach is the occurrence of thousands 

 of the tiny Cyamium minutum. This species is " gregarious among 

 seaweeds and under stones at low water," and " has a high northern 

 range ; but its southern distribution is limited"*. The other species 

 are common on the western coasts of Europe, and inhabit the littoral 

 zone. They are all to be found, with one exception, in Mr. Damon's 

 list of the shells of the Weymouth coast f. 



The beach on the west cliff is very thick and massive, but contains 

 very few shells. Mr. E. Cunniugton, who was with me in 1863, found 

 one specimen of Buccinum undatum, var. ; and I obtained a few 

 fragments of Mytilus ; but we found no others. 



The shingle of the raised beach is composed, in great part, of 

 chalk flints, with which are mixed some pebbles of the harder beds 

 and of the flint of the Portland rocks, together with others of a more 

 distant origin, the following being the order of relative frequency 

 and character of the pebbles forming the shingle, with the source 

 whence they are derived : — 



1 . Subangular fragments of flint . . . . , Chalk. 



2. Chert Upper Greensand. 



3. Ferruginous grit and sandstone 1 ^ TerU aHe S . 



4. Hard sandstone J 



5. Eed and purple sandstone ~j 



6. Grey and red quartzite pebbles I New Bed Sandstone 



7. Dark-red porphyry with large crystals of felspar f and its conglomerates. 

 8- Light-red porphyry with small ditto j 



9. Micaceous sandstone , Devonian? 



10. Light-red granite Cornwall? 



With these I found on the east side two large boulders, one of which 

 might be referred to a Tertiary sandstone, and the other to the Calca- 

 reous Grit. 



Deposits over the Raised Beach. 

 At the Bill the raised beach caps the cliff, and is not covered by 

 any other deposit, or only by a broken local debris ; but as we trace 



Fig. 2. — Section on top of cliff near the Boat-haul, Bill of Portland. 



Angular rubble, d, overlying 

 and mixing with the raised 

 beach, e. 





^ Portland beds. 



* Jeffreys's 'British Conchology,' vol. ii. p. 261. 



f Op. cit. p. 175. 



