92 Tlie America)) Geologist. Februar; isw 
in Missouri; and Archaean rocks arc present which are doI unlike those 
of the more typical areas in other parts of the American continent. 
This being the case, the normal and unchanged granitic rocks of the St. 
Francois region probably do not belong to the Archaean at all. hut to 
that recently established system which represents the enormous inter 
val of time between the formation of the truly azoic rocks and the dep 
osition of the lowest Cambrian. 
Recapitulating briefly, it may he stated that: 
1. The granites and porphyries are very closely related genetically,, 
and are to he regarded as fades of the same magma. 
2. Whatever may have been their origin, whether from a few or main 
points of extravasation, the present relations of the two are that the 
porphyry is an upper and surface facies of the granite, the thickness of 
the former being variable, having been originally unequally developed 
in different places and subsequently modified by both ancienl and re 
cent erosion. 
3. The present geographic distribution of the granites and porphy- 
ries is the outcome of very recent changes in the topographic configura- 
tion and is not <>f very ancient origin, as it appears to have been usuallj 
regarded. 
4. The existing areal relations of the principal masses of the acid 
rocks may he traced directly to the systematic ami widespread physio 
graphic effects of recent orogenic action. 
5. An element of uncertainty regarding the geological age of the 
massive crystalline rocks now prevails, and an exact determination maj 
always remain a problem. 
fi. The basal complex of'Archaean schists exists in the region within 
a very moderate distance beneath the highest Paleozoics. It differs 
widely in lithological characters from the crystallines usually referred 
to that age in the State, but closely approaches the more typical Ar- 
chaean rocks of other districts. 
Tllust rations of the Dynamic Metamorphism of Anorthosites ami re- 
lated rocks in the Adirondack*. J. F. Kemp, Columbia College, New 
York City. The high central peaks of the Adirondacks and the larger 
outlying ridges consist of anorthosite. a coarsely crystalline rock that is 
nearly pure labradorite. Though described as norite in earlier reports, 
it is noticeably poor or entirely lacking in ferro-magnesian silicates. In 
the course of a fairly extensive reconnoissance of the principal portion 
of the mountains, the writer has met hut a limited exposure of the an 
orthosites in an uncrushed condition. Specimens of such were shown, 
and beginning with these as a starting point the gradual development 
of crushed rims was shown, which, at hist barely discernible, increase 
until the original crystals of labradorite are but small nuclei. The ex- 
treme is a "pulp anorthosite," with no nuclei. The passage into gneis 
soid forms, through augen -gneisses, and with a rich development of 
garnets, was also illustrated. The final result is a thinly laminated 
gneiss. ( !omments on the areal distribution of these types were added . 
From a series of basic gabbros a gradual passage was shown, bj speci 
mens, into gneissoid types in the same exposure. 
