FOREIGN CORRESPONDENcr. 
245 
a couple fif yard;? from llic sides of Iho erupted trap-rock. In general, 
this change has Ijcen greatest ■where basalt and dolerite have heen 
ejected. The metamorphisni undergone by limestone, in these circiun- 
stances, includes a change of str\icture and the formation of certain 
minerals. Some calcareous strata have become hard and compact in 
those parts which have been pnshed up by trap-rocks ; others have 
taken a fragmentary, or even a prismatic structure — but only when 
they are argillaceons or siliceous. The prisms thus formed in limestones 
are not so well defined as those we observe in other varieties of rocks ; 
for instance, in sandstones, &c. The limestone of the Pyrenees has 
become cavernous or cellular by the metamorphic action of diorite. 
" Limestone," says jNI. Delesse, " generally becomes crystalline by 
metamorphism ; its colour becomes paler, and often exceedingly 
white." This reminds us that, some tune ago, we found that certain 
limestones, which were remarkable for their whiteness, and Avhich had 
been modified in structure by metamorjihism, contained a notable 
quantity of magnesia, which must perhaps be atti'ibuted to the contact 
of the eruptive rock. The analysis, made at the same time, of a 
greenish-yellow compact dolomite geive me protoxide of iron and 
magnesia, besides lime, in such proportion that a certain quantity of 
protoxide of iron seems to have been substituted for an equivalent 
quantity of magnesia. 
When a trap-rock has exercised metamorphic action upon a stratimi 
of limestone, M. Pelesse oljservcs th it the density of the latter has 
augmented considerably ; and in the vicinity of the eruptive rock are 
found mineral species produced by its influence, amongst others, 
oxide of iron, oxide of manganese, magnetic pyrites, brucite, dolomite, 
calcareous spar, clilorite, pyroxene, garnet, idocrase, gehlenite, &c. We 
find, also, in vems, injected, as it M'cre, through the limestone, 
barytine, celestme, oligiste, pyrites, galena, blemlc, copper-pyrites, and 
some others. 
M. Delesse has observed, also, that gypsum has been acted upon 
l)y metamorphism 2nuch in the same way as limestone ; thus, it 
has been observed in some cases to have become crystalline, and to 
contain oligiste and even iron-glance (carbonate of iron). AVe will 
reserve for a future paper INI. Delesse's remarks on the metamorphism 
of sandstones and argillaceous rocks. 
Professor Scacchi,- of Naples, has lately addressed a lettt-i' io the 
