Geology and Mineralogy. 221 
considerations of the isothermals for ice water. The place of 
this “hot ice” would seem to be represented by the prelongetions 
upward of the ice isothermals beyond the horizontal line to where 
they meet the line of no pressure. The critical point, which is 
roughly fixed at 14°C, would then be above the limit to the tem- 
perature of hot ice in a vacuum, “It is also pointed out that the 
sealing wax type of melting is probably similar to the change of 
ice into water below the lower, or above the gee critical points, 
if these exist.”— Phil. Mag., July, 1881, pp. 32-4 or. 
II GEroLtocy AND MINERALOGY. 
1. Geology of the Province of Minas Geraes.—From two im- 
portant memoirs published by Prof. Henrique Gorceix in the 
Annaes da Escola de Minas de Owro Preto, noticed in our last, 
we condense the roilowing fs account of the g geology of the central 
part e the province of Minas Geraes, Brazil. 
reater part of the central portion of the province of Minas 
Gunes 1s constituted by the great chain appropriately named Serro 
do Espinhago. This chain is formed principally of quartzose and 
schistose rocks, to which are joined granitic gneiss and even true 
granites, mica ’schists, dikes and intercalated beds of diorite and | 
finally small deposits | of anomalous rocks containing tourmalines, - 
disthene and other minerals. 
grains of hyaline quartz wihont cement. e quartz in these 
rocks are united two other substances, a rue mineral and mica- 
ceous iron which serve to characterize two principal geological 
horizons. The inferior division of the quartzites is characterized 
green color. These "quattdian are known by the e of ita- 
columites and are in the lower division chivacearaet by a 
schistose or flaggy structure. 
n the quartzites with the green substance two subdivisions are 
with an easterly inclination. Both divisions are traversed by 
auriferous veins, in which the Pacis is generally common iron 
ae or arsenical i iron 
sively of quartz, the gold is in larger grains but very irregularly 
disseminated in the vein rock. 
