Geological Collections. 63 



A lapidary, by attending to the above directions, will find no difficulty in re- 

 ducing any piece of petrified wood to that degree of thinness sufficient to render 

 its structure visible ; and any one, even without the aid of the mechanism em- 

 ployed by the lapidary, may accomplish that object by attending to the following 

 directions : — 



The position of the fibres of the wood having been ascertained, let a thin piece 

 be chipped off" by a blow of a hammer, in a direction perpendicular to the length 

 of the fibres. Let the chip thus obtained be cemented to any small bit of wood 

 by common lapidaries' cement (a compound of 1 part bees' wax, 1 part pitch, 4 

 parts resin, 16 parts of a mixture of brick-dust and whitening,) to enable the 

 operator to hold it firmly while the grinding is going on. That side of the chip 

 which approaches nearest to a perpendicular to the length of the fibres, must be 

 ground flat, by giving it a rapid circular motion with the hand, on a piece of sheet- 

 lead lying horizontally on a table, and supplied with a little emery, size No. 1., 

 moistened with water. When the emery ceases to act, the muddy matter re- 

 maining may be removed, and a fresh portion of emery applied ; and this must 

 be repeated until the surface of the chip has become perfectly flat. The sheet 

 of lead must then be removed, and a piece of flat sheet-copper substituted, and 

 the surface of the chip ground as smooth as may be, by flower of emery, freed 

 from its coarser parts. The surface may then be polished by friction with crocus 

 or rotten-stone, on a transverse section of any soft wood. 



When the polishing is finished, the chip must be detached from the wood to 

 which it was cemented, and the polished surface cemented by Canada balsam to 

 a piece of plate-glass, in the manner above described, and then ground thin, and 

 polished as before. 



Connexion of Diseases with the Rock Formations of a Country — In March 

 last, M. de Caumont laid before the Linnjean Society of Normandy, some remarks 

 on the influence possessed by the geological nature of the surface on the produc- 

 tion of certain diseases. 



Amongst a great many of the communes of Calvados, in France, near to each 

 other, and exposed to the same climatic influences, there is one which is particu- 

 larly liable to fever. Nearly the whole of these communes are situated upon lias 

 and red marl, and some other clayey formations, which retain at the surface a hu- 

 midity favourable for the formation of fogs. On the contrary, the communes 

 situated on rocks having a loose texture, and which permit the rain water to 

 escape more easily, such as the great oolite, chalky Sec, or which do not present 

 any beds capable of arresting the course of the water, as granite, and certain 

 slates, appear less liable to fevers. It results from these general considerations, 

 that the soil, by its greater or less hygroscopic quality, may have an eflTect on the 

 state of health, by favouring more or less the development of certain diseases. 

 M. de Caumont does not regard this observation as new, but communicates it 

 with the view of ascertaining in what proportions (every thing being equal), the 

 fevers and other maladies are developed in the principal geological regions of Cal- 

 vados ; for example in that of granite, slate, limestone, clay, &c. — Journal de 

 Geologie, No. I., p. 102. 



Fossil Floras. — Brongniart imagines that his several fossil floras are entirely 

 different from each other. He supposes that a general marine inundation has 

 always separated these floras from each other; consequently he is obliged to main- 

 tain that there are no vegetables, or only marine plants, in the deposits of rocks 

 that separate his four periods. This opinion is advocated by some geologists, 

 but rejected by others, Boue says, in the Journal de Geologie, t. i. p. 179, 

 JVofe, " M. Voltz and I reply, that, in proceeding from what is known, it is in 

 the nature of things that the arenaceous deposits or continental alluvium should 

 contain only land plants, and that the opposite should be the case with the cal- 

 careous deposits, with the exception of the modern fresh water deposits, since they 



