T?"OTES Als"!) QTJEEIES. 



149 



alluvium." The glaciers still occupied for a long time the deepest valleys, 

 and prevented their being filled with alluvial deposits ; then they melted, and 

 the Lakes Maggiore, Como, and Lecco, Orta and Iseo were formed. This 

 was the fourth and last jpaH of the glacial epoch, which gradually merged 

 into the present period. 



NOTES AND QUEKIES. 



CoNVEBSiox or Chalk into Maeble. — Gustav Eose has been making 

 new experiments on the deportment of carbonate of lime at high tempera- 

 tures, both with and without fluxes ;* and, from their results, he has arrived 

 at the conclusion that rhombohedral carbonate of lime is never a direct 

 product. 



According to the experiments of Sir James HaD,made in 1804, this has 

 been directly produced when chalk and compact limestone were exposed 

 to a high temperature under great pressure. 



Hall's experiment has therefore been repeated by MM. Eose and Sie- 

 mans. A gun-barrel was charged with dry elutriated chalk, rammed into 

 a compact mass, and the gun-barrel then hermetically sealed at both ends, 

 and exposed to the heat of one of M. Siemans' gas-furnaces. During the 

 experiment the gun-barrel sprung, and in the crack there appeared a faint 

 blue flame, evidently of carbonic oxide. The gun-barrel was then removed 

 from the furnace, and on opening it the chalk was found converted into a 

 light bluish-white coherent mass, slightly lustrous on the fracture, and with 

 cracks running through the whole. The surface was covered with a snow- 

 white, earthy, well-defined crust, and the cracks were lined with white 

 earthy particles ; these, as well as the crust, were composed of caustic lime. 

 Xhe compact mass, however, proved, on examination, to be unchanged 

 in chemical properties ; and in physical properties, though seemingly 

 changed, when examined under the microscope, it showed the same small 

 globules, and identically the same properties, as the unignited amorphous 

 chalk. Although somewhat more coherent, the chalk was not materially 

 altered, and in nowise converted into crystalline calcite. Another exjjeri- 

 ment was made with fragments of rhombohedral calc-spar, but was also in- 

 terrupted by the rupture of the gun-barrel. 



M. Eose considers, from these experiments, that chalk or compact lime- 

 stone cannot be converted into crj^stalline limestone or calc-spar by expo- 

 sure to a high temperature in closed vessels ; and, as a general fact, that 

 rhombohedral carbonate of lime is not formed in the dry way. He also 

 observes that, on comparing accurately the description of Hall's experi- 

 ments and Bucholz's observations incidentally made in the production 

 of caustic lime from chalk, probably they obtained results similar to his 

 own, and that the slightly coherent, but otherwise unaltered mass, was er- 

 roneously considered to be crystalline marble. But what is most singular 

 is, that notwithstanding Hall's experiment has been quoted and use made 

 of it, not only in explaining geological phenomena, but in serving as 

 the foundation of theories, it was never repeated or confirmed ; and the 

 experiments of M. Eose show it at least to have been hasty, although we 

 do not think M. Eose's have been as complete nor as long continued as 



* For an account of Herr Rose's experiments, see IVansactions of the Berlin Aca- 

 demy; Poggemlorf, Aunalen, c. xi. 156 ; and Silliman's Journal, xxxii. 112. 



