Dresser — Geology of JBrome Mountain. 355 



The place of the rock in the quantitative classification is as 

 follows : 



Class I, Persalane 



Order 5, Can ad are 

 Rang 1, Nordmorkase 

 Subrang 4, Nordmarkose 

 In structure it is megascopically granitic and, therefore, 

 becomes a grano-nordmarkose. It, too, is approximately norma- 

 tive. The chief departure of the norm from the mode is in 

 the alkali feldspars, which in the rock are in the form of micro- 

 perthite. 



Laurdalose. — This is a porphyritic rock having a greenish 

 matrix and a few phenocrysts of light gray color. 



In the microscopic section the rock is seen to be porphyritic 

 with a felsitic base. The phenocrysts are found to oe feld- 

 spar, generally of the character of that mineral in the nord- 

 markose. No plagioclase was certainly seen. Part of the 

 feldspar appears to be pure orthoclase but more possesses the 

 mottled character of cryptoperthite. Patches of granular f eld- 

 spathic-looking material are also numerous and are prominent 

 in the cryptocrystalline ground mass of the rock. Granular 

 ferromagnesian minerals are also found in some of these aggre- 

 gates. 



Magnetite and apatite in small amount are also present. 

 Sodalite appears in bluish individuals having rounded or poly- 

 gonal outlines. It is perfectly isotropic, showing no pleo- 

 chroism, even with a gypsum plate producing red of the first 

 order, and yields no interference figure in condensed light. 

 The dust-like inclusions characteristic of this mineral too are 

 noticeable. A little chlorite and a few individuals of biotite 

 are also seen. 



XI. x. XII. 



Si0 2 _ 55-68 59-96 55*65 



A1 2 3 20-39 19-12 2006 



Fe 2 3 ._. 2-10 1-85 3-45 



FeO 1-95 1-73 1-25 



MgO ._ -80 -65 -78 



CaO r 1-92 2-24 1-45 



Na 2 9-18 6 98 8*99 



K 2 5-34 4-91 6-07 



Ti0 2 -60 -66 



P 2 6 -06 -14 



MnO -31 -49 



HO 150 1-10 1'51 



99-83 100-17 99-21 



XI. Laurdalose, Brome. Analysis by M. F. Connor. 



X. Pulaskite, Shefford (Laurvikose), by M. F. Connor. 

 XII. Tinguaite, Hedrum, Norway (Laurdalite). Analysis by V. 

 Schemlck. Described by W. C. Brogger. (''Chemical 

 Analyses of Igneous Rocks," H. S. Washington.) 



