Merrill/J 
456 
[April 5, 
The specimen was reported to me as infusible, though swelling 
slightly before the blow-pipe. It was not decomposed by strong 
sulphuric acid, though a slight amount of iron appeared to be dis- 
solved out of it. 
The schist is, therefore, hydrous. Chemically, (if we may 
regard these partial analyses as furnishing any clue) it would 
seem to be either a margarodite which is considered to be 
often, if not always, a product of the hydration of muscovite, 1 or 
perhaps a mica intermediate between margarodite and paragonite. 2 
In a thin section, recently prepared, many of the ledge-formed 
sections of the mica showed the diverging fibres at the ends, 
which is characteristic for paragonite. 3 
Under the diorites (of Prof. Zirkel’s Report), specimen No. 
184, from Agate Pass, Cortez Range, is regarded by Mr. Wads- 
worth as a granite. 4 Since I find that the rock carries much more 
hornblende than mica, and that plagioclase prevails over ortho- 
clase, this seems to me to be a very ordinary diorite bearing both 
quartz and mica. But it is so well known that diorites pass 
gradually over into granites, and vice versa , that such cases will 
often be properly decided differently by different lithologists and 
without reflecting discredit upon either determination. The 
granite of the Agate Pass illustrates this. Zirkel called it a gran- 
ite 5 and Mr. Wadsworth approves the determination 6 ; but Mr. 
King prefers to consider it as a granitoid modification of the sur- 
rounding diorite. 7 There is probably but little to argue against 
either view, on purely lithological grounds. 
Mr. Wadsworth’s determination of No. 184 as a granite seems 
objectionable to me, since the rock appears to be on the diorite 
side of the line, with its prevailing hornblende and plagioclase. 
No. 183 from Mill Creek Canon, Mr. Wadsworth regards as also 
a granite. 8 Mr. King considers this as an intermediate link between 
1 In margarodite the water is generally considered as basic, but it is best also to con- 
sider the water in paragonite as basic; see Dana’s Mineralogy, 5th ed. p.487; also 
Zirkel’s 10th ed. of Naumann’s “Elemente der Mineralogie,” S. 554. 
2 Dana’s Mineralogy, 5th ed. p. 487. 
3 Rosenbusch, “ Mikroskop. Phys. der Min. u. Gest.” Bd. I, S. 376. 
4 These Proceedings, Vol. xxi. p. 255. 
5 Report, p. 48. 
6 These Proceedings, Vol. xxi, p. 255. 
7 Vol. i, p. 72, Report of the Geol. Expl. Fortieth Parallel. 
8 These Proceedings, Vol. xxi, p. 256. 
