FOREIGN CORRESPONDEXCE. 
251 
These specimens were accompanied by a full mineralogical 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 yalley 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 yalley of the ancient lake of Taguatagua on which new light 
has been thro^vn by the study of the region aboye mentioned. 
On Density and Hardness considered as distinctive characters of 
Metalloides and Metals. 
M. Marcel de Serres has communicated an important paper to the 
French Academy on the aboye subject. " The classes, orders, and 
families, which haye 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 diyided naturally into gases, liquids, and 
solids, the latter into soft (apalides) and hard (schlerides), 
" The soi't 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 diyides 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 diyided 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 phosphoms, 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 Thecodontosauriis. 
M. P. Geryais has communicated a notice of the first discoyery of 
the remains of this animal in France. M. Dumortici, of Lyons, who 
forwarded the specimens to him, found them at Chappon (Ain). M, 
Geryais refers to the characters of the genus, as stated by Messrs. 
Riley and Stutchbury in their memoir on the Th. autiquus of the 
