AUTHORS’ ABSTRACTS 377 
The fact that the general surface facies of the acid rock has been 
actually eroded is shown by several high isolated hills which rise out of 
the granite area. Some of these, as Knob Lick for instance, are still 
capped by porphyry. They show further that the granite, to a depth 
of over 400 feet has been removed in addition to the surface shell of 
porphyry. 
To recapitulate : 
1. The granites and porphyries are very closely related geneti- 
cally, and are to be considered as facies of the same acid magma. 
2. Whatever may have been their origin, whether from a few or 
many points of extravasation, the present relations of the two are that 
the porphyry is an upper and surface facies of the granite, the thick- 
ness of the former being variable, having been originally unequally 
developed in different places and subsequently modified both ancient 
and recent erosion. 
3. The present geographic distribution of the granites and 
porphyries is the outcome of very recent changes in the topographic 
configuration and not of very ancient origin as it has been usually 
regarded. 
4. The existing areal relations of the principal masses of the acid 
rocks may be traced directly to the systematic and wide-spread physio- 
graphic effects arising from recent orogenic action. 
5. An element of uncertainty regarding the geological age of the 
massive crystalline rocks now prevails and an exact determination may 
always remain a problem yet to be solved. 
6. The basal complex of Archean schists exists in the state within 
a very moderate distance beneath the highest Paleozoics. It differs 
widely in lithological characters from the crystallines usually referred 
to that age, but closely approaches the more typical Archean rocks of 
other districts. 
Syentte-Gneiss (Leopard Rock) from the Apatite Region of Ottawa County, 
Canada. By C. H. Gorpon. Bull. Geol. Soc. Am., Vol. VIL., 
pp- 95-134. Rochester, December 1895." 
In the collections of the Canadian Geological Survey at the World’s 
Fair there were displayed specimens of a rock showing a peculiar 
«Thesis presented for degree of Doctor of Philosophy, University of Chicago, 
June 1895. 
