1895.] Petrography. 569 
tween the plagioclase and augites, and are thought to have originated 
from the alteration of nepheline. 
Migration of Crystals from a Younger to an Older Rock. 
—It has long been assumed, that of two igneous rocks in contact, that 
containing crystals peculiar to the other was necessarily younger than 
the latter. Cole,‘ however, shows that crystals may be floated away 
into a pre-existing rock of a low degree of fusibility from one of a 
higher degree which has intruded it. At Glasdrumman Port, County 
Down, Ireland, a dyke of eurite is flanked on both sides by dykes of 
basaltic andesite, of which the andesites are unquestionably the older 
rocks, since the eurite on its contact with them encloses fragments torn 
from their sides. The eurite contains porphyritic crystals of pink 
orthoclase, while the andesite is normally devoid of them. Near its 
contact with the former rock, however, crystals exactly like those in the 
eurite are occasionally found in the andesite. Crystals of quartz and 
feldspar have also often been floated from the eurite into the detached 
fragments of the andesite. The invading rock has melted the ground- 
mass of the andesite and has left its larger crystals scattered through a 
matrix made up largely of molten andesite intermingled with some 
eurite substance. 
Notes.—In a report accompanying an excellent geological map of 
Essex Co., Mass., Sears® describes briefly the following rocks: Horn- 
blende granitites, granophyric granitites with a flowage structure, augite- 
nepheline syenites, hornblende diorites, quartz-augite-diorites, musco- 
vite-biotite-granites, norites, quartz porphyries, peridotites, gneisses, 
both igneous and clastic, bostonite and tinguaite dykes and various 
effusive rocks, 
A series of chemical analyses of the gneissoid granites, granite por- 
phyries and porphyrites of the Bachergebirge in Stiermark, has been 
made by Pontoni® in order to discover whether all the granite porphy- 
ries, that form great dyke masses in the region, have the same compo- 
sition or not, and whether the small porphyrite dykes that cut the 
granite are like the granites and the granite porphyries or are unlike 
them. The conclusion reached is to the effect that the granite porphy- 
ries are identical with the gneissoid granites of the region, and that the 
porphyrites are independent intrusives. . 
*Scient. Trans. Roy. Dub. Soc., Vol. V, Ser. II, p. 239. 
> Bull. Essex Inst., XX VI, 1894. 
ê Min. u. Petrog. Mitth., XIV, p. 360. 
