424 Pirsson — Petrography of Tripyramid Mountain. 



cutting gabbros, and which have been considered aplitic in 

 character, like hecrhachite for example. The fabric is that 

 characteristic of lamprophyres, rather than of aplites. 



Chemical Composition. — A chemical analysis of the rock has 

 been made for me by Dr. Ralph W. Langley, formerly assistant 

 in the Sheffield Laboratory, and to whom my thanks are due 

 in this connection. It is given in No. 1 of the following table 

 and with it are also given analyses of some dike rocks which 

 are of interest for comparison. 



Analyses of Dike Rocks. 



No. 



I 



II 



III 



52-95 



IV 

 41-94 



V 



VI 



VII 



VIII 



IX 



Si0 2 ... 



50-75 



50-59 



50-50 



51-70 



47-21 



0-846 



0-843 



Al a O, .. 



17-31 



17-74 



14-96 



1536 



17-71 



19-39 



20-52 



0-170 



0-174 



Fe s O, .. 



2-08 



3-54 



2-44 



3-27 



5-41 



2-54 



7-48 



0-013 



0-022 



FeO ... 



8-13 



7-45 



7-03 



9-89 



4-02 



6-44 



5-32 



0-113 



0-104 



MgO... 



3-48 



3-92 



3-86 



5-01 



3-33 



4-64 



4-16 



0-087 



0-098 



CaO ... 



6-77 



6-85 



6-76 



9-47 



7-91 



8-95 



8-63 



0-121 



0-122 



Na s O .. 



4-14 



4-25 



4-95 



5-15 



5-52 



4-07 



5-17 



0-066 



0-068 



K 2 U.._. 



2-87 



2-79 



1-64 



0-19 



3-02 



0-83 



0-33 



0-031 



0-030 



H.O+ - 



0-56 



0-55 



0-55 



3-29 



0-45 



0-92 



0-34 







H.O- . 



... 







- - - 











0-15 



0-10 



..-■ 



... 



00, — . 



none 











2-47 

















- - - 



TiO, ... 



3-05 



2-60 



3-90 



4-15 



1-91 



0-14 



? 



0-038 



0-033 



PA — 



0-10 



0-27 



0-76 



? 



0-92 



0-37 



0-46 



... 



0-002 



MnO... 



tr 



99-14 



tr 



10 0-5 5 



tr 



0-25 



— 





— 











Total .. 



100-16 



100-44 



100-70 



100-68 



99-21 









II 

 III. 



IV. 



V. 

 VI. 



VII. 



VIII. 

 IX. 



(Andose), dike near the Black Cascade, Slide Brook, 

 Waterville, N. H. R. W. Langley, analyst. 



(Andose), dike at Norway Rapids, Slide Brook, Water- 

 ville, N. H. C. J. Monahan, analyst. 



Spessartite ? (hornblende akerose), Belknap Mts, N. H. 

 (Pirsson & Washington, this Jour., vol. xxii, p. 455, 

 1906). Washington, analyst. 



Camptonite (camptonose), Livermore Falls, Campton, 

 N. H. (G. W. Hawes, this Jour. (3), vol. xxvii, 

 p. 150, 1879). 



Essexite, Rongstock, Bohemia (Hibsch, Tscher. Mitt. 

 xix, Heft I, 1899). R. Pohl, analyst. 



Luciite-porphyrite (beerbachose), Ernsthofen, Oden- 

 wald, Hesse (Chelius, Notbl. f. Erdk., xviii, p. 15, 

 1897). W. Sonne, analyst. 



Beerbachite (beerbachose), Frankenstein, Odenwald, 

 Hesse (Chelius & Klemm, Erl. z. Geol. Karte Hes- 

 sen, x, p. 39, 1896). R. Marzahn, analyst. 



Molecular proportions of No. I. 



Molecular proportions of No. II. 



