246 



SCIENCE-GOSSIP, 



GEOLOGY 





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



Scarcity of Terrestrial Remains. — A little 

 thought will enable ihe enquiring geologist 

 to realise how slight are the chances of terrestrial 

 animals leaving their hard parts in a fossilised condi- 

 tion in water-formed strata. When a land-living 

 organism dies, its body rapidly decomposes, its 

 bony portions finally obeying the same law. Unless 

 covered up , by strata, comparatively few of such 

 remains reach an area where sedimentary forma- 

 tions are being laid down. Some may fall into the 

 bed of a running river, and may be there entombed, or 

 be transported to the sea to be there preserved. Other 

 remains become buried in chemically-formed deposits, 

 such as deposits of travertine or in stalagmite. Other 

 creatures lose their lives in peat-bogs, and so become 

 preserved. The action of the wind in forming sand- 

 dunes may sometimes be responsible for the covering 

 of remains, although it is not possible to determine 

 with certainty any ancient rocks whose origin can be 

 attributed to aeolian action. Landslips may have also 

 been responsible in times past for the preservation of 

 forms of terrestrial life, whilst occasionally the dust and 

 ashes of volcanoes are known to have entombed such 

 remains. But putting all these possible causes together, 

 their results are insignificant as compared with those 

 resulting from the many opportunities to be found in 

 every stream, river, sea, and ocean, for the 

 entombment of marine creatures in the sedimentary 

 deposits there forming. Mere absence of certain 

 forms of terrestrial life in a deposit, is, therefore, 

 no evidence that those forms did not exist. The 

 real cause for wonder is that the geological record 

 is as perfect as it is. 



Calcite and Aragonite. — The extent to which 

 shells of molluscs formed of carbonate of lime resist 

 the tendency to disappear under the solvent agency of 

 water charged with carbonic acid, depends not only 

 upon the time during which they are exposed to 

 such action, but also on the form in which the 

 carbonate of lime exists. If the shell be of aragonite, 

 this will be found to have disappeared in strata 

 where shells composed of calcite often remain intact. 

 Aragoniteisharder and heavier (sp. gr. , 2.93) than calcite 

 (sp. gr., 2.77). Pectitnailus glycimeris is an example 

 . of an aragonite shell, such shells being opaque, having 

 1 chalky appearance and a compact structure. Among 

 calcite shells is the fossil Pec/en opercularis, which is 

 translucent, and its surface is compact, but its 

 interior is porous. All the Brachiopoda and the 

 Echinodermata have calcite skeletons, as well as 

 Oslrea and Pecten amongst the L'ammellibranchs ; 

 but the common mussel (Mytilus editlis), Pinna and 

 Spondylitis have an inner layer of aragonite, and an 

 outer one of calcite. 



The Great Crosby Boulder. — In the transac- 

 tions of the Liverpool Geological Society, 1898-1899, 

 is a description of the erection in the village of Great 

 Crosby of the great Gypsum Boulder, by T. Mellard 

 Reade, F.G.S. This mass of gypsum is estimated to 

 weigh 18 tons, and to contain 280 cubic feet. It was 

 discovered in 189S in the brickyard of Mr. E. Peters, 



in Cook's Lane, Great Crosby. The offer of the 

 proprietor to present it to the local District Council 

 was accepted, with the result that it has now been 

 erected in the village on a suitable pedestal, and has 

 been carefully oriented so as to correspond with its 

 original position where found. Mr. Reade is to be 

 congratulated on the successful completion of the 

 work. 



Chalk of Harefiei.d. — Harefield is noted for 

 its cement works, where there is a good section of 

 Upper Chalk, overlaid by London Clay and Wool- 

 wich Beds. The chalk exposed is about sixty feet 

 thick, with marked layers of flints almost continuous 

 every four feet. Fossilsare not easy to find, but I have 

 been able to procure Caryophyllia cylindracea, 

 Porosphaera, Terebella lewesiensis, Onychocdla 

 laniarcki, Alembranipora, Dianchora, Pecten 

 cretosus, P. nitidus, Ostrea acutirostris, Bourgue- 

 ticrinus, spines of Cidaris perornata, C. sceptrifera, 

 Micraster coranguinuni, Pollicipes glaber, and 

 Ananchytes ovatns. — C. Fletcher Brown, 3, Topsfield 

 Parade, Crouch End, N. 



Noble Opal in Somerset. — There can be no 

 doubt that the whole of Somerset is strongly 

 glaciated, the evidence being naturally plainer in the 

 hilly parts. I detected a good example of glacial 

 drift, amongst many such cases, on the shore 

 between Kiloe and Watchet. Below the red beds 

 of the Keuper on the shore there is a vast accumula- 

 tion of red pebbles of the same colour as the Keuper 

 hard beds but I found on a careful examination 

 they are without a doubt of Devonian origin. I 

 followed them in their course down the long slope 

 from the Quantoch range, finding them visibly 

 scratched and relatively unworn, and on the 

 main road to Watchet the source of the 

 supply was discovered, the hard Devonian slates. 

 Near Radstock an opal pebble occurred in the drift. 

 I have discovered the origin of these "noble opal" 

 pebbles. They occur sparingly in the lower beds of 

 the Inferior Oolite, which contain concretionary 

 masses and derived materials. They are in fact con- 

 glomerative, although not of a strongly accented type. 

 The source of supply is therefore near. This does 

 not detract from its glacial origin, of which there is 

 abundant proof in scratched blocks, etc., some of 

 them probably of millstone grit age. These must 

 have been transported for at least a distance of five 

 miles. The course of the local drift seems to have 

 been largely from the chalk range of Wiltshire, which 

 lacks a name, as an increase of flint debris can be 

 noted in the fields, as one approaches that range from 

 here. As many of these flints are variously fractured, 

 the geologist invites the archaeologist to reconsider 

 some of his flakes in the light of glacial erosion. An 

 archaeologist on the other side might invite his 

 geologist brother to study the difference between the 

 erosion of the plough and that of ice. This challenge 

 he has begun to accept, to the large increase of accu- 

 rate knowledge on both sides, and to the great profit 

 of many hitherto dubious points in Somersetshire 

 geology. — T. Stock, Frome Hill, Radstock. 



Geological Exchange Meetings. — Various ex- 

 changes were arranged at Science-Gossip offices at 

 the meeting announced last month. The next meeting 

 for exchanges will take place on January 10th, from 

 5 p.m. to 7 p.m., when readers are invited to attend 

 with their specimens. The departmental editor will 

 be present. Specimens may be sent to his care, and 

 in this case it should be stated what is desired in 

 exchange. It is hoped that as many readers as 

 possible will attend. 



