Geology and Mineralogy. 148 
4, Hruptive Liga apt rocks of Lake Snperior.—Mr. 
RapuareLt Pumpetty has an elaborate memoir in volume xiii of 
eding e American Academ Boston, on ‘“ the 
dark brownish black, augitic rocks, without hornblende in any 0 
the varieties, but often ‘chry solitic. The triclinic feldspar is for 
the most part labradorite or anorthite, so that the chemical com- 
position is to this extent essentially that of doleryte or a diabase, 
or a chrysolitic variety of these basic rocks, They are generally 
more or less altered and —— chloritic ; wis they are fre- 
quently amygdaloidal--a very common act with Be or 
chloritic eruptive rocks. “Tita iron or magnetite and apatite 
the Pi of te rock in the vicinity of veins sud cavities; the 
relations of each result of Gicviatou: “through various stages, to 
the mineral from which it sprung and the further successive 
among those of chrysolite, hydrous iron oxide, a green serpentine- 
like mineral, and hematite. 
e following are some of the cases mentioned of the order of 
dspar: 
rehnite, chlorite, orthoclase, epidote, quartz. 
(2.) Prehnite, eee epidote, — native copper. 
(3.) Prehnite, e epidote, calcite, qua 
— Prehnite chlorite, Se eiisisaes-ortheciaae being a product 
er pre 
_ In the ‘filling of amygdaloidal ahs there have been formed 
i succession, as pseudomorphs after prehnite, chlorite, calcite, 
i it 
