IGNEOUS ROCKS 311 



These analyses give the following norms : 



I. II. 



Quartz 41.28 27.84 



Orthoclase 8.90 12.23 



Albite 23.58 23.06 



Anorthite 18.07 22.24 



Diopside 0.25 1.36 



Hypersthene .... 5.13 8.80 



Magnetite 1.39 2.32 



Ilmenite 0.91 



Apatite 0.34 



H 2 0.- • !-0 6 125 



99.76 100.45 



The more acid facies of the Port Deposit granite is a biotite-grano- 

 susquehannose* (class I, order 3, rang 3, subrang 4). This means that 

 the salic constituents preponderate ; that of the salic constituents quartz 

 and feldspar are present in nearly equal amounts ; that of the feldspars 

 the alkali molecules are equal to the lime molecules ; that of the alkalies 

 soda is dominant, and, finally, that the texture is megascopically 

 hypautomorphic granular, and that the only abnormative mineral present 

 in the rock is biotite. 



The more basic facies falls in class II, order 1, rang 3, subrang 4. 

 Like the acid type, it is dosodic and alkalicalcic, but differs from the 

 other facies in the fact that the salic minerals are merely dominant, but 

 not preponderating, and feldspar is dominant over quartz. The texture 

 of the rock is hypautomorphic granular, biotite is the only abnormative 

 mineral present, and is a critical mineral. The name of the rock is there- 

 fore a biotite-grano-tonalose. 



GABBRO (GABBRO, HYPERSTHENE-GABBRO, NORITE, META-GABBRO) 



Distribution. — This is a great igneous body which, with many ramifi- 

 cations and varying petrographic facies, intrudes into the Atlantic belt 

 of crystallines from Virginia to New York. 



*The name susquehannose is suggested by the writer for subrang 4 of rang 3, order 3, class I. 

 This subrang, in the absence of any strong claims for preeminence on the part of the species 

 falling in it, was left unnamed by the authors of the quantitative system of nomenclature. 



The appropriateness of susquehannose lies not only in the fact that large quarries in this rock 

 species have long been worked on the Susquehanna river, but also that calcic granites of this 

 general type are especially abundant in the region drained by that stream. The attention of the 

 writer has been called in this connection by Dr H. S. Washington to the fact that there is a zone 

 of calcic rocks striking parallel with the Atlantic coast and showing in Labrador, eastern Canada, 

 Adirondacks, Pennsylvania, and Maryland. East of this belt is a zone of sodic rocks showing in 

 Ontario, New Hampshire, eastern Massachusetts, New Jersey (Beemerville), and farther south in 

 Georgia, Texas, and Tamaulipas, Mexico. 



The high calcic content of the other igneous types of the Pennsylvania district will be made 

 evident in their discussion. 



