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SCIENCE-GOSSIP. 





Win. 



CONDUCTED BY EDWARD A. MARTIN, F.G.S. 



To whom all Notes, Articles and material relating to Geology. 



and intended for Scienxe-Gossip, are, in the first instance, to 



be addressed at 69, Bensham Manor Road, Thornton Heath. 



As a result of the decomposition of organic 

 substances, " homus " becomes charged with what 

 are known as the homus acids (crenic, opocrenic, 

 ulmic, etc.), and these acting upon a subsoil of 

 limestone, such as chalk, cause its disintegration, 

 and it is probably owing to their action that the 

 surface of the chalk is so often seen to be broken by 

 holes like inverted cones, filled with rubble result- 

 ing from the destruction of the chalk. The irregu- 

 larity of the surface would be owing to the rock 

 yielding to the solvent acids in different degrees in 

 different places. 



A. J. Jukes-Browne has pointed out, in describ- 

 ing the geology of the town of Devizes before the 

 Geologists' Association, a peculiarity in the Lower 

 Chalk, which here rests upon six or seven feet 

 of passage-beds or chloritic marl. Under the 

 microscope the carbonate of lime is seen to be 

 accompanied by minute discs and globules of 

 silica, together with silicious spicules of sponges. 

 It includes mineral (? quartz) particles, glauconitic 

 grains, fragments of shells (silica), cavities filled 

 with silica and residuary spicules. At Eastcott 

 it contains hard cherty nodules, which may be 

 regarded as imperfectly formed flints. 



No one who has collected fossils from the gault 

 can have failed to notice that many of them 

 have become wholly pyritised. Large lumps of 

 pyrites can also be easily obtained which bear no 

 resemblance to fossil forms at all. Roft says that 

 pyrites is formed by the conversion of sulphate of 

 iron into the sulphide by organic matter, and also 

 from " traces of ferrous carbonate, mixed with 

 sulphates of the alkalies and alkaline earths, in the 

 presence of organic substances. Its formation is 

 still to be observed in peat-bogs, in deposits from 

 mineral springs, from waters of mines containing 

 sulphate of iron, and from sea-water, where the 

 coasts furnish soluble iron compounds." The de- 

 composing animal matter in the shells would give 

 rise to organic acids which would reduce a sulphate 

 by removing its oxygen, and deposit a sulphide of 

 iron, in many cases even removing the calcite of 

 the shell itself, and replacing it molecule by 

 molecule by pyrites. 



Foreign Boulders in Chalk. — The discovery 

 of boulders and pebbles of granite, green schist, and 

 quartz in the Chalk at various times, has always 

 excited considerable interest. Probably such dis- 

 coveries are not really rare, but the stones found 

 are distributed amongst numerous private collec- 

 tions. In 1857 the famous " Purley boulder" was 

 discovered in Haling Pit, South Croydon. This 

 was composed of syenite, and weighed nearly forty 

 pounds. It was accompanied in the matrix by 

 pebbles and fine sand, and owing to its weight its 

 carriage across the cretaceous sea is not thought 

 to be explicable except by the agency of floating 



ice. Other boulders of smaller size have since 

 been excavated from the Chalk, the neighbourhood 

 of Norwich having yielded various specimens. 

 Among those more recently discovered are two 

 which were obtained from the Middle Chalk of 

 Betchworth, in Surrey, by Mr. W. P. D. Stebbing, 

 F.G.S. The two boulders in question were of 

 granite, although different in character, and were 

 both very much weathered. They weighed 7 lbs. 

 7 oz. and 3 lbs. 12 oz. respectively, and measured, 

 the one 5-8 in. x 6-25 in. x 4-125 in., and the 

 other, 36 in. x 58 in. x 4'5 in. The trans- 

 portation of these boulders, which Professor 

 Bonney judged might be of Scandinavian origin, 

 was attributable to one of four causes : by adhesion 

 to seaweed, driftwood, by marine animals, or ice. 

 It was particularly interesting to notice that to the 

 largest, valves of Spondylus latus and Serpula, were 

 still attached. In the presence of these and other 

 larger boulders in the Chalk, we have undoubted 

 evidence that the sea in which was laid down the 

 Middle Chalk was occasionally traversed by stray 

 icebergs. 



Permanence of Ocean Basins. — Amongst the 

 many preconceived notions which have in recent 

 years been abandoned by modern geologists is the 

 opinion that our ocean-beds have in former geolo- 

 gical times formed portions of continental areas, 

 and the theory has gained ground that although 

 the boundary lines have shifted their positions 

 very considerably, yet, in the main, where there 

 are oceans now, there have always, more or less, 

 been oceanic areas. But there is a tendency in 

 this also to go to extremes. Dr. Blandford 

 remarked seven years ago, that " whilst the general 

 permanence of ocean-basins and continental areas 

 cannot be said to be established on anything like 

 proof, the general evidence in favour of this view 

 is very strong." Some land areas, on the other 

 hand, have within comparatively recent times 

 been submerged beneath more than a thousand 

 fathoms of water, whilst " sea- bottoms, now over a 

 thousand feet deep, must have been land in part of 

 the Tertiary era." Besides, there is every evidence 

 to prove that there have been formerly land connec- 

 tions across what are now broad and deep oceans. 



Geologists will probably for a very long time 

 continue to inveigh against the indefensible titles 

 which characterise the formations known as the 

 Upper and Lower Greensands. When Webster 

 proposed the terms in 1S24, he little knew how 

 great a trouble they would be to geologists in the 

 future. Green sand the Lower Greensand seldom 

 is, and Godwin-Austen, in 1S50, proposed for it the 

 French equivalent title, namely "Neocomian," 

 although it is now found the Neocomian is the 

 equivalent of our Wealden, the " Aptian " being 

 that of the Lower Greensand. "Vectian" has 

 since been proposed by Jukes-Browne, and has 

 everything in favour of its adoption, except 

 popular use. So far as the Upper Greensand is 

 concerned, any name which is proposed for it must 

 include also the Gault clay, since the latter is now 

 recognised as being merely a deep-sea equivalent 

 of the former. Fitton proposed, in 1824, the name 

 of " Merstham Beds." In 1S92 Jukes-Browne pro- 

 posed " Devisian " (Devizes), there being no French 

 title which distinctly described the French equiva- 

 lent strata. It seems very doubtful whether any 

 new titles are now likely to find favour. Upper 

 and Lower Greensand are such firmly-rooted names 

 that even if we wish it it is improbable that they will 

 cease to be used by the general body of geologists. 



