Haworth on ihe Archcean Geology of Missouri. 381 
more, so this one must not be overlooked in the classification, 
although it is the only representative of the melaphyres. The 
following scheme represents the different types found, the num- 
bers given being those of the hand specimens which are fair 
representatives of the several types. The classification is slightly 
different from that given by Rosenbusch in that all the dyke 
rocks are here placed under one general head for convenience, 
while he would place them under two. 
Diabase 
and 
diabase 
porphjryte 
Quartz- 
bear 
rt?:- ( 
. ■ \ Quartz-diabase, 23c, 36^. 
ring ^ ) oj> o o 
Quartz 
and 
-^ olivine 
free. 
Non-uralitized^ Wantin< 
Holocrjstalline 
Uralitized 
Uralite diabase, 
236, 339- 
r Non-uralitized — diabase porphyry tes, 
Glassy < 290. 
[^Uralitized — uralite-porphyryte, 388. 
^,. . f Holocrvstalline -^ Olivine-diabase. 
Olivine J - ' 
° [^Glassy -^ Melaphyre. 
Summary. 
1" The Missoviri Archaean is interesting on account of its 
isolated position, and on account of the simple character of its 
rocks. 2". The rocks may be divided into three general classes. 
A, Granites; B, Porphyries of different kinds; C, Dyke rocks 
which are diabase and dlabase-porphyrytes. 3". The granites 
are mainly granltites with a small amount of biotite, but they 
grade on the one hand into a quartz, feldspar granite — or gran- 
itell of some American geologists and on the other into a horn- 
blende-bearing granitite. 4". The feldspar enlargements of 
the granites probably resulted from a secondary growth, during 
the effusive period of idiomorphic crystals formed during the 
intertelluric stage. 5". The idiomorphic quartz and feldspar 
crystals, the micropegmatite, and the granophyric structure show 
that the structure of the granites approaches the porphvritic, 
and the gradation of the one into the other is easily traced. 6". 
The evidence of fumcrole action at the Silver Mines consists in 
the alteration of the granite wall rock of the vein and the for- 
mation of topaz, wolframite, lepidolite, and fluorite. 7"- The 
