1891. ] NEW YORK ACADEMY OF SCIENCES. 21 
In I all the iron was estimated as Fe,O,. The excess of potash 
over soda in I and II is exceptional. While the rather abundant 
biotite of I in part accounts for it, the amount of this mineral is 
hardly enough to furnish it all. The silica is also lower than in 
the Triassic diabases, which afford about 50-53 per cent. 
Olivine appears in a few dikes fresh enough to recognize, and an 
alteration-product is shown by a great many more which may have 
resulted from it. In other respects the olivine diabases are not 
different from those without this mineral. 
Diabase, including olivine diabase, is an extremely common dike 
rock in the Archean rocks of Canada and the northern United 
States, and it is probable that most of those simply recorded as trap 
belong also with this species. 
The Camptonites. 
The name camptonite was originally employed by Rosenbusch 
to designate those dike rocks which consist of hornblende and plagio- 
clase, but varving amounts of augite are also often present. They 
lack the ophitic structure of diabase in that the hornblende or augite > 
is prevailingly idiomorphic. The diabases of dikes thus pass into 
them by the idiomorphie development of the dark silicates. In the 
Lake Champlain region there are dikes of both the augitic and the 
hornblendic variety. We have employed the name augite-camp- 
tonite when wishing to make a distinction. 
The camptonites consist of brown basaltic hornblende, augite, 
plagioclase, magnetite, and occasionally a. little intermingled g lassy 
matter. The minerals are markedly panidiomorphie and the large 
hornblendes and augites give at times a porphyritic character. The 
hornblende is the most conspicuous and attractive component. It 
is strongly pleochroic, brown to yellow, and, in distinction from 
the augite, shows no zonal structure. A small second generation 
consists of minute acicular cr ystals, which are a miniature repro- 
duction of the larger forms. The augite likewise forms two genera- 
tions. The older and larger consists of zonal prismatic erystals with 
dark green cores and light yellow rims, which may differ 10° in 
extinction. The second generation are minute and acicular. The 
plagioclase is less perfectly developed than the bisilicates. Several 
camptonites contain abundant olivine. 
The camptonites all contain less than 45 per cent. SiO, in this 
region, but in other respects present great variability. They do 
not afford more than 6 per cent. of alkalies, with soda usually in 
excess. The following table illustrates the range of composition :— 
