Petrography of Shefford Mountain. — Dresser. 211 
vsbergyte type. It is apparently closely related to the acmite- 
trachyte of Profs. Wolfif and Tarr. (Bull. Mus. Comp. Zool., 
Cambridge, 1893) afterwards re-named by Prof. Wolff as 
tinguayte, var. solvsbergyte. In that rock, however, the bi- 
silicates are in the form of segerine and aiigite intergrown, in- 
stead of a single mineral of intermediate composition as at 
Shefford. 
I 
II 
III 
IV 
SiOo 
59.96 
60.03 
59.01 
58.70 
TiO. 
.66 
.81 
trace 
AI2O3 
19.12 
20.76 
18.18 
19.26 
Fes O3 
1.85 
4.01 
1.63 
3.37 
Fe02 
1.73 
.75 
3,65 
.58 
MnO 
.49 
trace 
.03 
.10 
CaO 
2.24 
2.62 
2.40 
1.41 
BaO 
.12 
MgO 
.65 
.80 
1.05 
.76 
KoO 
4.91 
5.48 
5.34 
4.53 
NaoO 
6.98 
5.96 
7.03 
■8.55 
P2O5 
.14 
.07 
.10 
CO2 
none 
SO3 
.08 
none 
CI 
.14 
none 
.12 
H2O 
1.10 
.59 
.50 
2.57 
100.17 101.07 99.98 100.00 
I. Pulaskyte, Shefford. Analysis by Connor. 
II. Pulaskyte, Fourch Mountain, Arkansas. Analysis by Brackett 
and Smith. 
III. Umptekyte, Red Hill, Moulteuborough, New Hampshire. Cited 
by Rosenbusch, loc. cit, 
IV. Solvsbergyte (Acmite Tracheyte), Shield's River, Crazy Moun- 
tains, Montana. Analysis by Melville. Described by Wolflf 
and Tarr. 
Contact Fades. 
The endomorphic contact facies of each of these rocks is 
marked by an increase in the proportion of the ferromagnesian 
constituents and the appearance of nepheline and sodalite 
amongst the accessory constituents. The essexyte thus be- 
comes a very dark rock of which hornblende alone sometimes 
makes up about one-half a'^nd frequently approaches very 
nearly to the character of theralyte. The nordmarkyte shows 
also a great increase of the basic constituents, especially bio- 
tite. The feldspar ton changes from microperthite to krypto- 
