400 JULIEN 



suggested by an observation in Delaware county, in south- 

 eastern Pennsylvania, on a series of schistose and gneissic rocks 

 considered to be more recent than the Hudson River group, 

 probably altered Devonian : " Throughout a greater portion of 

 the gneissic and schistose belt the cleavage has been, in many 

 cases, mistaken for the bedding of the rock. . . . The cleavage 

 dip varies from 75 to 90 degrees. . . . The true bedding of the 

 measures is nearly horizontal and undulating. The so-called 



* bottoms ' are more or less distinct lines of separation through- 

 out the gneissic mass, and are the true lines of bedding. These 



* bottoms ' usually maintain their relative distance from each 

 other and cross the cleavage planes at angles which are usually 

 uniform in each locality. . . . In most of the quarries through- 

 out southern Delaware county the ' bottoms ' or bedding is 

 sharply defined." ^ Such distinction of the foliation of schists 

 from their true bedding would of course establish the uncon- 

 formity of all igneous rocks intercalated along the foliation. 



In this connection it has been stated, concerning the gabbros 

 and gabbro-diorites of Delaware : ** I have looked carefully for 

 any other evidence of bedding except that coincident with the 

 cleavage, but have found none. The so-called ' bottoms ' . . . 

 could not distinctly be made out in Delaware. Planes which 

 might be taken for these v/ere irregular and not continuous and 

 correspond more to joints than to planes of bedding. ... It 

 must be noted, however, that if w^e consider the true planes of 

 bedding of the mica-schists to lie nearly horizontal, then the 

 thin outlying lenticular masses of gabbro-diorite . . . which 

 are apparently interbedded with micaceous rock, must be re- 

 garded more strongly than ever as intruded bodies, cutting 

 across the stratification. That these rocks are of this character 

 the author is strongly inclined to believe." ^ 



On Manhattan Island, in the upper bed of micaceous schists 

 and gneisses, in which the diorite-schists he enclosed, division- 

 planes and joints intersect the foliation. But those at low 

 angles are occasional, irregular, too obscure to be recognizable 



iC. E. Hall, Second Geol. Surv. Penn., Pt.^I, C. 5, 1885, 2-3. 

 2F. D. Chester, Bull. 59, U. S. Geol. Surv.^ 1890, 39-40. 



