FOREIGN CORRESPONDENCE. 



251 



These specimens were accompanied by a full miner alogical notice 

 of each, and a letter addressed to M. Elie de Beaumont, by M. 

 Domeyko, announcing that he has sent two cases of fossil-bones, 

 found in the same locality he had explored the preceeding year at 

 Taguatagua. He also gave a description of a recent valley containing 

 bones of Pachyderms, situated at the foot of the Andes, and presenting 

 the same features as the great formation two or three hundred leagues 

 on the other side of the range. This circumstance will, perhaps, 

 throw some light on the true epoch of the relationship of this district 

 to the last changes of the Andes M. Domeyko also sends a note 

 on the valley of the ancient lake of Taguatagua on which new light 

 has been thrown by the study of the region above mentioned. 



On Density and Hardness considered as distinctive diameters of 

 Metalloides and Metals. 



M. Marcel de Serres has communicated an important paper to the 

 French Academy on the above subject. " The classes, orders, and 

 families, which have been established in the classification of simple 

 bodies, considered in regard to their hardness and density, appear 

 to be founded on sundry rules, which the comparison of these proper- 

 ties has furnished. 



" The metalloides are divided naturally into gases, liquids, and 

 solids, the latter into soft (apalides) and hard (schlerides). 



" The soft metalloides, with one exception (phosphorus), are denser 

 than the hard ones : it is principally by the degree of hardness that 

 the two orders may be distinguished." 



M. Serres then proceeds to inquire whether the difference between 

 the density and hardness of the metals is as decided as in the case of 

 the metalloides. For this purpose he divides the metals into — 1. 

 Heteropsides, which are the lightest bodies among the metallic sub- 

 stances, being in some cases less dense than water. 2. Allopsides, 

 which comprise the hardest bodies in nature, often the schleride 

 metalloides, indicated by the No. 10, in the scale of Mohs. 3. 

 Autopsides, which are again divided into perfect metals and common 

 metals. 



From the tables we learn that among the metalloides phosphorus 

 is the least, and tellurium the most dense ; and that phosphorus, again, 

 is the softest and diamond the hardest. 



Among the metals stilbite is the least, and iridium the most dense ; 

 while asbestos is the softest, and emerald the hardest. 



On the Extinct Genus Tliecodontosanrus. 



M. P. Gervais has communicated a notice of the first discovery of 

 the remains of this animal in France. M. Dumortici, of Lyons, who 

 forwarded the specimens to him, found them at Chappon (Ain) . M. 

 Gervais refers to the characters of the genus, as stated by Messrs. 

 Riley and Stutchbury in their memoir on the Th. antiqims of the 



