430 J U LIEN 



rocks, in part of detrital origin — mica schist and gneiss, dolo- 

 mitic marble, quartzite and banded biotite-muscovite gneisses 

 — displaying the same petrographic facies and sequence as at 

 Manhattan Island, with similar extreme plication, and also 

 penetrated by vast quantities of eruptive materials. 



The correlation of these crystallines from the Washington to 

 the New York area has been recently so clearly defined ^ as to 

 require no repetition for my present purpose. But the inference 

 that the differences in alteration of the rocks of these two tracts 

 in Maryland, and among the same crystallines along the Appa- 

 lachian belt, have been due to contact metamorphism, is, in my 

 opinion, for many reasons improbable and untenable. It would 

 appear rather as a belt of orogenic disturbance and metamorphism, 

 to which the eruptives themselves have owed their more exten- 

 sive extrusion and through which they have shared deformation 

 and change with the sediments they invaded. They have been 

 classified under three types : 



(i) Intermediate, the most ancient, consisting of hypersthene- 

 gabbro, gabbro-diorite passing into hornblende schist, quartz- 

 gabbro, norite, diorite, hornblendite and hornblende-biotite- 

 quartz-gabbro. (2) Basic, comprising pyroxenite, Iherzolite, 

 cortlandtite and serpentine. (3) Acid, comprising binary granite, 

 granitite, hornblende-granite, granite-porphyry, augen granite- 

 gneiss, felsite and pegmatite. It is further stated : " The areal 

 distribution of these gabbro masses ... is believed by the 

 author to indicate that the various occurrences represent what 

 was once an immense gabbro sheet extending from Laurel, 

 Maryland, to the Schuylkill river, a distance of fully 85 miles, 

 with an exposed breadth of at least 1 5 miles. Through this 

 great sheet of gabbro were apparently intruded the granites and 

 later metarhyolites and pegmatites, the whole constituting one 

 great series of igneous activity." ^ Reference has been made ^ to 

 the close alliance of these intrusives to the more limited series 

 at Manhattan Island, and to the more complete metamorphism 



^ E. B. Mathews, A7?i. Jotir. Sci., (4), XVII, 1904, 142-146. 

 2 Matthews, loc, cit., 155. 

 ''Julien, loc. cit., 485-486. 



