No. 1.] DANA — SOME POINTS IN LITHOLOGY. 47 



The relation to the feldspar group iodieates the occurrence of 

 special geological circumstances, which turned feldspathic mate- 

 rial into saussurite. The circumstance that determined the 

 crystallization or metamorphism may have produced, in its in- 

 cipient stage, soda- lime feldspar ; but it ended in making a large 

 part, or the whole, saussurite. Moreover the hornblende has been 

 shown to be, in part at least, pseudomorphous after pyroxene ; 

 so that the foliated ingredient bears like evidence of this mode 

 of origin. Consequently saussurite rocks not only differ molecu- 

 larly from any labradorite or feldspar rock, but are indications 

 of peculiar geological operations on a large scale ; and this con- 

 nected with other differences, makes it desirable to distiniruish 

 such rocks by a special name. The saussurite and not the foli- 

 ated mineral is the chief ingredient on which the distinction rests. 



Euphotide is therefore a different rock from any, consisting 

 of cleavahle labradorite and pyroxene or hornblende, both on 

 mineralogical and geological grounds. The foliated condition of 

 the latter constituent is not reason enough for overlooking the 

 more fundamental differences. As the name gahhro has covered 

 rocks of so different kinds, lithology would be freer of ambigui- 

 ties without it. 



The true labradoriteand-pyroxene rock of Scandinavia, the 

 Adirondacks, British America, and other regions, sometimes 

 called Noryte — the third kind of gabbro — has the chemical and 

 mineralogical constitution of diabase or doleryte. But it differs 

 from these in its granitoid aspect and geological relations, and 

 is of metamorphic origin ; and as it is of wide geographical dis- 

 tribution, geology seems to require for it a distinct name, and 

 noryte is an appropriate one. 



The pyroxene, though generally foliated, is not always so. 

 When, in place of pyroxene, there is true hypersthene, a mineral 

 of different composition and character, as at St. Paul's, Labrador, 

 the rock is then rightly called Hypersthenyte, and this name is 

 so used by Zirkel. 



3. PorpJiyritic Structure. — Porphyry naturally took the posi- 

 tion of a species in the mineralogy of the ancients. But it is 

 now well known, and generally admitted, that the porphyritic 

 structure is largely due to conditions attending the former tem- 

 perature and cooling of the rock-mass, and distinguishes only 

 varieties. But still it is usual to find dioryte divided, for its 

 primary subdivisions, into ordinary dioryte and dioryte-porphyry; 



