THE EASTERN AREA. 411 



in most respects precisel\- like the dialiases in the main area to the west- 

 ward, (lescril)e(l on pp. 3r)0-3r)4, a description of them will not be given in 

 detail, only points of difference being mentioned. 



The augite of this area frequently shows twinning. The twinning is 

 of the form most common, the twins each being in two parts and the com- 

 position plane the ortho})inacoid. 



The enlargement of augite and hornblende alluded to, pp. 3.n3,354, as 

 occurring in some of the diabases at the extreme west end of the western 

 area, here most beautifully occurs. The cases of enlargement of both the 

 augite and hornblende are finer than any known to the westward. Such a 

 renewed 2"i'f>wt]i (»f hornblende in a kersautite has been described liy Fried- 

 rich Becke.' • 



The following quotation is fronx his description: 



Die jirimilren fompacteii Horubleude-Ki-ystalle sind .selir hiiufig von einer Riude 

 uingeben, welclie aus sti in "differ griiiier Hornblende besteht, die g.in/. niit der 

 Hornblende des TJralit iibereinstiinnit. In Quersclmitten beobaclitet man die dnreh 

 Kern and Hiille fjleieliniiissig fortsetzendeii Spaltrisse. Mitnnter hat der so weiter 

 gewaelisene Krystall andeie Ivrystalllliielien in der Prismenzone, als der Kern. In 

 Lilng.sclinitten sielit man den eompacteu Kern mit Biindeln i)arallel angewachsenei- 

 Hoi-n1)lendeuadeln ver.sehen, welclie sicli weiterhin zn divergireuden Biiselieln auf 

 lo.sen. * * * Die Art des Anftretens dieserFortwaelisunffen llisst keinen Zweitel, 

 dass wiihrend der Ansbildnng dieser Portwai'hsnngen niei-lianiselie liewegnngon 

 innerhalb dieses Gesteius nicht melir stattgefanden liabeu. (P. 1.58.) 



It thus appeal^ that Becke discovered in 1883 the enlargement by 

 secondary growth of individuals of hornblende in an eruptive rock, this 

 change having taken place subsequent to its consolidation. 1 have described 

 the enlargement of hornblende by second growth in certain fragmental 

 rocks in northeastern Minnesota.^ Here the change is of greater impor 

 tance than in eruptive rocks, for it explains in part at least the induratit)n 

 of such clastic sediments. However, in the eruptives under consideration 

 I have met with cases of new growths occun-ing upon augite and horn- 

 blende, which are corroborative of and add sometliing to the observations 



' Tschermak's Min. und Petr. Mitth., vol. \', p.art it, 1883, in a p.appr entitled " Ernptivgesteine 

 ans der Gneisflforrantion de.s niederoatorreichiscben Waldviertels." 



'C. R. Van Ilise: Knlargements of Ili)rnlili-ude Fragments. Am. Jmir. Sci., :id series, 1XK5, vol. 

 XXX, pp. 231-235. 



