HARD WICKE ' 5 £ CIENCE- G O SSI P. 



i5 



level, the average level above the sea being about 

 200 feet, whilst the Shakespeare Cliff boring was 

 commenced almost at sea-level. 



In the skeleton map which accompanies this article, 

 the -lines of section which have been illustrated by 

 the diagram have been shown. 



Another section which should have our considera- 

 tion is one which is represented only by three borings, 

 viz., Burford, Ware, and Harwich. This section 

 does not certainly pass through London, but as the 

 question of underground London has the greater 

 interest for many people, because the question of 

 possible sub-London coal-beds is involved in it, it 

 should not be omitted, since at Harwich a continua- 

 of the palaeozoic land-surface is shown in the 

 appearance of undoubted coal-measures at 1029 

 feet. The curves in Fig. 15, may possibly represent 

 the general direction of the strata, or the general rise 

 and fall of a line connecting the numerous isolated old 

 land-basins which probably formed the old surface. 



A noteworthy feature in connection with the short 

 section in. Fig. 16, is that 10 feet of lower green- 

 sand rocks are reported from the Richmond 

 Waterworks, and are spoken of by Mr. Whitaker 

 in his work on the geology of the London area. 

 Professor Judd was, however, understood to say at a 

 lecture delivered in February last at Richmond, that 

 the "greensand wedge of rocks did not appear even 

 so far north as Richmond, so that it would appear as 

 though he were in doubt as to the identity of the 

 10 feet of rocks in question. 



It cannot, however, be very far south of Richmond 

 or Streatham where the wedge appears, and probably if 

 ever the water-supply from the chalk fails the borough 

 of Croydon, an ample supply would be obtained from 

 the underground lower greensand, which would 

 probably be successfully encountered there. 



In concluding these sketches of what is known of 

 the beds beneath London, I must acknowledge my 

 indebtedness to Mr. Whitaker, F.G.S., who has 

 kindly pointed out a slight mistake in my last article. 

 In referring to the diagrams it will be seen that at 

 Caterham I have placed supposed Jurassic beds im- 

 mediately.beneath the lower greensand. No doubt were 

 the boring continued there below the present 814 feet, 

 Wealden rocks would first of all be encountered, since 

 the outcrop of these takes place at a very short distance 

 southwards, viz., at Reigate. As this is, however, 

 outside of the London boundary, it makes but 

 little difference in connection with the purpose for 

 which the diagrams were specially prepared. 



It is understood that the geologists of the East 

 Anglian counties hope shortly to be able to commence 

 boring operations with a view to finding coal-measures, 

 and considerable promises of support have been 

 received. The results of boring here, together with 

 those being carried on in Kent, should increase to an 

 appreciable extent our knowledge of the deep-seated 

 geology of the south and south-east of England. 



NOTES ON THE 

 CONCHOLOGICAL SOCIETY'S NEW LIST 

 OF BRITISH MOLLUSCA. 



By T. D. A. Cockerell. 



THE Conchological Society's new list, which had 

 for some time been expected to appear, was 

 duly published in the "Journal of Conchology" for 

 April (issued June 3rd), and is no doubt by this time 

 in the possession of nearly every British collector or 

 student of mollusca. 



A critical list like this is a very different matter 

 from my " British Naturalist " Catalogue, which aimed 

 simply at giving all the recorded forms, except 

 absolute synonyms. The authors of the new list 

 have gone over the whole series of published names, 

 changing or dropping them whenever they thought 

 advisable, and adding some from their own know- 

 ledge. The result is sufficiently remarkable, for 

 although only thirty-eight varieties are added to those 

 listed in the "British Naturalist" Catalogue, over 

 three hundred and fifty names which have been applied 

 to varieties or mutations of British land and fresh- 

 water mollusca, are excluded ! Among these are 

 several which were earlier named, or introduced as 

 British, by the authors of the list. 



Messrs. Taylor, Roebuck, and Nelson have s}udied 

 the British Mollusca so closely for many years, that 

 probably nobody will question the value of a list com- 

 piled by them ; and if many are found who disagree 

 with some of its features, it is only because of the 

 wide divergences of opinion which exist, rendering 

 it impossible to produce a list that will suit every- 

 body. 



For my own part, I totally disagree with the 

 authors on the subject of varietal nomenclature, 

 believing that a very careful examination of all forms 

 of variation throughout the country is desirable, 

 and that for facility in recording and comparing 

 records, we must have names. Without elaborate 

 research of this kind, I do not believe we shall 

 succeed in solving in a satisfactory manner such 

 problems as present themselves, e.g. those relating to 

 the influence of environment, or to the divergence 

 from the continental type exhibited in these islands. 

 As Darwin observed, "I look at individual 

 differences, though of small interest to the systematise 

 as of the highest importance for us, as being the first 

 steps towards such slight varieties as are barely 

 thought worth recording in works on natural history. 

 And I look at varieties which are in any degree more 

 distinct and permanent, as steps towards more strongly 

 marked and permanent varieties ; and at the latter, 

 as leading to sub-species, and then to species." 

 (" Origin of Species," p. 41.) The deviations from 

 the typical form in any variable species may be classed 

 under three heads, as follows : 



