186 Scientific Intelligence — Geology and Mineralogy. 



zoic coal district. According to Goldfuss, who assigned the name 

 Archigosaurus Dechcni to the reptile thus found, it is a kind of a 

 crocodile-lizard, the skull not resembling that of the Emydosauri, 

 which are nearest to it in geological date, but that of the true croco- 

 diles now existing. At the same time, there are characters in the 

 skull, which is 6^ inches long (Rhine measure), shewing it to par- 

 take of the lizard. Regarding the skull to have formed the same 

 proportion to the entire reptile, as in the young crocodile, this speci- 

 men would have belonged to an individual measuring 3 feet 8 inches. 

 Mr Lyell mentioned the discovery by Dr King, in 1844, of rep- 

 tile foot-tracks upon sandstones in Pennsylvania, considered equiva- 

 lent to part of the palseozoic coal-measures of the British islands ; 

 indeed the Greensburg sandstone is stated to occur in the very midst 

 of the Appalachian coal-field, the main Pittsburg seam of coal being 

 worked 100 feet above it. — (Sir Henry T. De la Beche, V.P.R.S., 

 Anniversary Address.) 



12. On the Structure and I'eratology of Crystallised Bodies. 

 By M. A. Baudrimont (Comptes JRendus, Nov. 8, 1847, p. 668). 

 — M. Baudrimont gives the following table of observations made by 

 him on the cleavage of calc-spar. It is interesting, as shewing that 

 while the fact that the vertical axis is normally an axis of symmetry, 

 as demonstrated by the crystallisation, and by optical, therniome- 

 tric, and acoustic investigations, still extrinsic circumstances cause 

 some variations from perfect symmetry in the cleavage.* The cleav- 

 ages observed are as follow : — 



(1.) Parallel to the faces of the primary rhombohedron. 2. Paral- 

 lel to the longer diagonal of the primary faces. 3. Parallel to the 

 shorter diagonal of the primary faces. 4. Parallel to different se- 

 condary planes. 



(2.) Cleavage parallel to the primary rhombohedron. Equal in 

 three directions (normal) ; rare. Iceland Spar. Equal in two di- 

 rections; less rare. Unequal in three directions ; common. 



(3.) Cleavage parallel to the longer diagonal of the primary faces. 

 In a single direction ; quite common. In two directions, unequal ; 

 more rare. In three directions ; vej-y rare. 



Irised appearances and coloured bands are produced by this kind 

 of cleavage. In all cases, images are polarized in directions parallel 

 to the diagonals of the faces of the rhombohedron. 



(4.) Cleavage parallel to the smaller diagonal of the primary faces. 

 In one direction ; very rare. Produces a species of coloured rings. 

 M. Baudrimont gives details, shewing also that the lustre and trans- 



* It would add greatly to the value of these observations, if the mode of at- 

 tachment of the crystal to the sujjportiiig rock were mentioned, as the axis of 

 f.Uachmtnt (unless it were the vertical axis exactly) would be under a diflFerent 

 condition from the other homolofrous axes of the crystal. 



