192 



THE GEOLOGIST. 



the limestone of Yalos^nes ; the " ehoin batard " of Lyon; the " foie de 

 veau" of Bourgo^jne; the Sinemurien in part of D'Orbigny ; the " qua- 

 trieme eta^^e " of the Lias of D'Archiac ; the upper dolomite of Lombardy, 

 etc. In the tabular view which the author gives, the Etage Infraliasien 

 is placed below the zone of Ammonites BucJclandi, and is formed in the 

 following manner : — 



1. Zone of A mmonites angulatus. 



2. Zone of Ammonites planorhis. 



3. Zone of Terehratnla gregaria. 



4i. Zone of Bactryllium, reposing on 



THE KEUPER. 



Henceforth, if the author's views are correct, these Avicula contorta beds 

 would serve as the lower limit of the Jurassic formation, and will form a 

 datum line of great importance in studying the geology of the Alps. The 

 Essay appears to be an extract from the excellent memoir by the Abbe, 

 " The Palseontology of Lombardy." 



M. Morlot has given an account, in the ' Indicateur de Suisse,' of the 

 finding of a part of a nodule of pyrites amongst the remains of the lake- 

 dwellings of the Stone-age at "Robenhausen by M. Messikommer, which 

 was furrowed by striking it against some hard substance, probably for the 

 purpose of obtaining fire. Many fragments of pyrites have previously been 

 found at the same place and at Wangen. Another specimen, as large 

 as the first, and evidently used for the same purpose, has recently also 

 been found by M, Engelhardt, amongst a great number of different 

 antiquities, dating from the earliest ages to our own era, in a peat-bed at 

 Bonder Brarup, in Denmark. 



NOTES AND QUERIES. 



Cutting Diamonds. — There still seem to be, in the minds of most per- 

 sons, some wrong notions relative to the manner of cutting diamonds, and 

 especially this is the case in London. Although several notices and de- 

 scriptions of diamonds have appeared in various serials and magazines of 

 late, none of them describe the process of cutting, except in such a vague 

 and unintelligible manner as to impress upon the minds of readers a simi- 

 larity of the method of cutting, to that of other stones. The principle, it 

 is true, is somewhat the same, but the operation is distinctly different. It 

 is also generally stated, that the workmen have such a very perfect know- 

 ledge of the crystallography of the diamond as to enable them to cleave 

 it very readily. The fact is they know nothing whatever of crystallogra- 

 phy, -at least as a rule, — and only cleave the crystals by experience. As 

 to why a diamond should cleave in a certain direction, they cannot tell, 

 uor could they explain naIiv they strike it on one particular "spot in order 

 to do so. It is alsc) gcMun-ally stated that diamonds are cut on the ^v.n- 

 ciple of" diamond cut diamond," two crystals being rubbed together till 

 a facet is produced. They are certainly rubbed together to get them a 

 little into shai>e : but how ? If the reader rub two crystals of diamond 

 together, he will find that he hardly makes an impression on either; but 

 if the stones are inserted in metal and attached to a holder, and these held 

 in the hands, which are rested on a bench, the thumbs towards each other, 

 then it will be found that the mechanical pow er or leverage obtained is 

 very great, even sulfunent to crumble and break such hard material as 



