778 REGINALD ALDWORTH DALY 
igneous rocks are less likely to be altered by intrusive masses 
than are the more basic rocks. In the same way sedimentary 
rocks are in general more susceptible to contact metamorphism 
than the crystalline chists or than igneous rocks.* Pohlig noted 
important differential effects of the trachyte in the Siebengebirge. 
Fragments of gneiss enclosed in the eruptive rock were rela- 
tively unchanged as compared with inclusions of clay-slate in 
which andalusite and other metamorphic minerals were devel- 
oped.? Lehmann has described granulite inclusions in the gra- 
nite of Markersdorf which he found to be entirely unchanged by 
the granite.3 No student of contact-belts needs, however, to be 
reminded that in them there is pronounced selective metamor- 
phism depending upon the nature of the rocks invaded. Those 
which have advanced furthest in the direction of mineralogical 
stability will usually be the rocks which are least altered. IH, 
then, there had been regional metamorphism of the country-rock 
before a given intrusion occurred, such terranes will tend to be 
without distinct zones of alteration. Such is the case with the 
New Hampshire rocks. In the sequel the chief evidence for this 
conclusion will be given, but we can anticipate somewhat by 
stating the fact that the same series of schists which are cut by 
the porphyritic granite are just as thoroughly crystalline many 
miles from the porphyritic granite as they are in its immediate 
vicinity. Moreover, they attained this crystalline character in 
the process of mountain-building and not by any kind of local 
thermo metamorphism induced by underlying areas of the por- 
phyritic granite.t The eminent schistosity of these rocks was 
anterior to the granitic intrusion, and it is an effect concomitant 
with the recrystallization. Thus it was a series of terranes already 
regionally metamorphosed that were cut by the porphyritic gran- 
ite. They had reached a state of approximate mineralogical 
equilibrium and but little rearrangement of the constituent 
elements was possible by mere contact action. 
*Cf. HUDLEsTON, Address Pres. Geol. Soc., 1894; Q. J. Geol. Soc., p. 121. 
?Tschermak’s Mitth., 1880-1, p. 353. 
3 Untersuch. iiber die Entsteh., der altkryst. Schiefergesteine, 1884, p. 7. 
4Cf. BARROW, Q. J. Geol. Soc., 1893, p. 352. 
