HARDWICKKS SCIENCE-GOSSIP. 



129 



any length of time in the study, for new forms are 

 continually turning up which have a tendency more 

 or less to upset settled decisions. I should recommend 

 any one who may have a number of dubious forms, 

 which cannot be referred to any marked and estab- 

 lished variety, to simply put them on one side in a 

 drawer, and label them as intermediates, adding 

 locality, whether from pond or running water, with 

 elate or other circumstances. I have tried hard to 

 discover some means of knowing when a shell is 

 mature, but have failed. I think, however, when a 

 diell shows more than twelve principal growth lines, it 

 is approaching maturity. These lines in A. cygnea 

 are generally raised into ridges, and some shells 

 ■exhibit forty or fifty, not reckoning the finer secondary 

 Hines which are smooth. In A. anatina (full grown) 

 ■smooth spaces without ridges or lines are considered 

 to be distinctive of the species. But there is great 

 discrepancy in the descriptions of Anodons by British 

 authors, for instance Macgillivray says that the shell 

 of A. anatina is very thin and brittle, whilst Tate 

 says it is thick. The same with illustrations, Jeffreys 

 has figured a shell on plate ii. (British Conchology) 

 which is named A . anatina, but Gray has figured a 

 -very similar form (p. 288, "Manual," 1840) which 

 is called A notion cygnens. 



A few notes on Unio tumidus and pictoriun are 



;reserved for a future number. 



Geo. Roberts. 



Loft house, Wakejield. 



THE PLIOCENE BEDS OF CORNWALL. 



PROBABLY the most important discovery in 

 English stratigraphical geology, within the 

 last few years, is that of a deposit of Pliocene age, at 

 St. Erth in Cornwall, far distant from the typical crag 

 areas. A resume of its more important features may 

 be of interest to the readers of this magazine. 



St. Erth is a village of between two and three 

 thousand inhabitants, three and a half miles south- 

 east of St. Ives, and two miles south-west of Hayle. 

 The deposit was first noticed by Mr. N. Whitley,* of 

 Truro, who however referred it to the Glacial period. 

 But the first detailed account of it was given by the 

 late Mr. S. V. Wood,t who referred it to the Pliocene 

 period, which has since been confirmed. 



The deposit is exposed in a pit near the Vicarage, 

 where the beds shown in the accompanying section 

 (Fig. 50) may be seen. The "head" is a clay with 

 fragments of various rocks, most likely a glacial de- 

 posit. " Growder " is a coarse ferruginous sand. The 

 blue clay is the most important bed, as it contains a 

 large number of well-preserved fossils. The yellow 

 clay above may be only a weathered part of the lower 

 deposit. The whole area of the deposit is less than 



* On the evidence of the Glacial Action in Cornwall (Royal 

 Geol. Soc. Cornwall, 1882). 

 •J- Quart. Journ. Geol. Soc, vol. xli. p. 65. 



an acre, so that it is perhaps scarcely to be wondered 

 that it was not discovered before. The shells being 

 preserved in a clay present a very different appearance 

 to the crag fossils, and, indeed, so resemble those 

 found in the eocene clays, that at first one feels in- 

 clined to place them in that formation ; but an 

 examination of the species soon dispels this idea. 



The following is a list of the more important 

 forms : — Fusits corneus, Lin. ; Columbella sulcata, 

 Sow. ; Nassa serrata, Broc. ; N. granulata, Sow. ; 

 Cyprcca avellana, Sow. ; Natica millepunctata, Lam. ; 

 Cerithium reticulation, Da Costa ; Turritella triplicata, 

 Broc. ; Rissoa reticulata, Mont. ; Trochus zizyphinus, 

 Lin. ; T. multislriatus, S. V. Wood ; Odostotnia 

 acuta, Jeff. ; O. rissoides, Han. ; O. plicata, Mont. ; 

 Calyptrcca Chinensis, Lin. ; Conovulus pyramidalis, 



f 



5^ 





o o o o o 00 o o 



\\ 







• •' d ,„f\ 



v Ait'-l^ 



Vegetable soil. 

 " Head," 2-6 feet. 



Yellow sand, 4-6 feet. 



"Growder." 

 Yellow clay, 6 feet. 



Blue clay, with fossils, 6 feet. 

 Quartz-pebbles. 



Fine quartzose sand, 10 feet. 



Elvan Dyke. 



Fig. S o.— Section at St. Erth (after Messrs. Kendall and Bell*. 



Sow. ; Ostrea edulis, Lin. ; Pecten maximus, Lin. ; 

 P. operculars, Lin. ; Pectunculus glycimcris, Lin. ; 

 Nucula nucleus, Lin. ; Cardium echinatum, Lin. ; 

 Lucina borealis, Lin. ; Cardita aculeata, Poli ; Artemis 

 exoleta, Lin. ; Tapes pullastra, Wood ; Mactra solida, 

 Lin. ; Mya arenaria, Lin. ; Solen ensis, Lin. 



Messrs. Kendall and Bell* have found 72 determin- 

 able species of Mollusca, and about 20 others which 

 appear to be new. Sponges, polyzoa, crustaceans, 

 echinoids, annelids, alcyonarians, holothurians, tuni- 

 cates, ostracods, and foraminifera also occur. Tuni- 

 cates have never before been found fossil ; the species 

 according to Dr. Herdman is closely allied t) 

 Leptoclinum teuue, obtained by the "Challenger." 

 The foraminifera are very abundant and beautifully 



* Quart. Journ. Geol. Soc, vol. xlii. p. 201. 



