Geology and Mineralogy. 463 
probably of the age of the Potsdam sandstone. The Report first 
gives a history of former geological investigations of the region 
and a full bibliography ; and then treats of the distribution of the 
rocks, their kinds and stratigraphy, and all with great thorough- 
ness. The enh part is specially interesting on account 
of the large amount of eruptive rocks in the Keweenian series, 
and ales the hae i excellence of the colored microscopic illus- 
trations. The basic eruptive rocks of the region are remarkable 
ne 
base, olivine-diabase, diabase-porphyrite (=porphyritic diabase), 
melaphyr, gabbro, and oliv ine-gabbro with anorthite rock. Pr 
fessor Irving remarks that “ all of the kinds, although distinct 
enough in the field are, cn mame conside red, but phases of 
one kind of work,” and plagioclase-augite e rocks, to which 
“the term ‘basalt,’ sentricted by Sescnlin sch to their younger 
equivalents, mi ht be not improperly used.” The diabase and 
hyr occur amygdaloidal, and figures on seolee s 311 and 
326 represent the layers of successive outflows with the lower 
half solid and the upper vesicular. e ga os are generally 
coarsely crystalline and sometimes contain orthoclase ; the others 
are of all grades of texture. The anorthite rock is a coarsely 
whi 
ting black gabbro and has included angular masses in the same 
rock. The acidic rocks are granite (one small locality) augite- 
syenyte and granulite “ porphgriti granite; quartziferous por- 
yry, quartzless porph and telsyte—which terms mean: 
felsyte, both meson nad Lie and quartzless (the quartz usually in 
distinct crystals), and either porphyritic with feldspar crystals 
or no elsyte rocks are mostly of a pale or deep re 
e subject of the origin of the minerals in the amygdaloidal 
cavities and their successive formation, so well investigated by 
Pumpelly, was ~ canst: tbe rae git = Prof. Irving, and only 
a statement of Pumpelly’s results ts 
he fr saicilicke rocks of the series are made of granitic and 
felsitic material, and in part of material from the other igneous 
rocks, but are nowhere true quar Aes + lua sete A indicat- 
‘tin es 
her the 
any part of the Candidas group of reat 1 Been or is older 
than its oldest beds, Prof. Irving leaves undecided, for the good 
