SO-CALLED PORPHYVRITIC GNEISS OF NEW HAMPSHIRE 793 
intrusive and certainly younger than the upper Devonian at any 
rate. 
Posterior to the schists, to the so-called protogines, and to 
other old eruptives on the one hand, the porphyritic granite is, 
of course, older than the aplitic and lamprophyric dikes which 
intersect it. It is also older than the Fitzwilliam granite, the 
hornblende granite stock of Mount Whiteface, the Franconia 
breccia,* and probably older than the complex stocks of the 
Waterville area. It is impossible with the facts now in hand to 
go further in fixing an epoch for these great intrusions. The 
porphyritic granite may even belong to the Tertiary. 
SUMMARY. 
Briefly stated, the chief conclusions which have been arrived 
at in the foregoing pages, are as follows: 
1. The so-called ‘ porphyritic gneiss” of New Hampshire is 
at least in the three most important areas, an eruptive porphyritic 
granite with a common tendency to develop planes of foliation. 
It is not to be regarded as indigenous, that is, as the pure 
fused product of the surrounding formations—a deep-seated 
exotic origin must be posited for the granite. The evidences for 
an igneous instrusive origin include the composition and struc- 
ture of the rock itself, the study of field-relations, the fluxional 
nature of the foliation, the uniformity of the rock in all its extent 
and the prevalence of secondary dikes and veins of injection 
apparently derived from the same magma. Besides _ these posi- 
tive facts, there are also those embodied in what may be termed 
negative evidence. It includes all those observations that have 
been made in which the peculiarities of the region and of each 
intrusion will explain why some of the usual criteria of eruptive 
origins are not perfectly fulfilled. Chief among them is the fact 
of small certain and undoubted metamorphic effects at contacts 
— one which we have seen can be readily understood from the 
characters of the invaded rocks. Lastly, the contacts at first 
sight equivocal prove to be intrusive contacts on comparative 
"Geolhrot Nei. Viol: ll, ps 257. 
