188 PETROLOGICAL ABSTRACTS AND REVIEWS 
practically vertical. It therefore probably also represents an eroded 
volcanic neck. 
ee Main INTRUSION IN EACH IN ORDER easy 
MouwuntTAINs IN OF OccCURRENCE Navas oF IDescaaanl as 
ORDER FROM INTRUSION BY S 
East TO WEST M ap 
No. 1 No. 2 No. 3 TES 
Shefford...... Essexite | Nordmarkite | Pulaskite | Laccolith | Dresser] 9.0 
Brome ane eaee Essexite to| Nordmarkite | Tinguaite | Laccolith | Dresser) 30.0 
theralite to nephelite 
syenite, 
and dikes 
Yamaska..... Wamaskatelpeisg os aes svat: |iie sugente ene Neck Young BOG 
; to essex- 
ite to 
akerite 
Rougemont...| Yamaskite |. Cele ce Male: Rae ak, Neck O’Neill | 9.5 
to essex- 
ite to 
rouge- 
montite 
Johnson...... Essexite to|....... Ein ohgital ea CHO Neck Adams | 0.77 
pulaskite 
St. Hilaire..:.| Essexite to| Nephelite- |.......... Neck O’Neill | 6.76 
rouvillite| | syenite 
Sie eaUMAOY, <4 6 || IDGHOSUO WO) Neco cous eeueelsouseonb oc Laccolith? | Dresser | 2.83 
syenite 
(umpte- 
kite) 
Mount Royal.| Essexite INephelitessrriasce eee Neck ? Adams 2.0 
syenite Laccolith ? | Buchan 
The rocks of St. Hilaire are essexite and nephelite-sodalite-syenite, 
with several varieties of each, and there are various dikes. Essexite 
was first intruded. At various places in it, brown hornblende becomes 
prominent. In one occurrence there is a very small amount of ferro- 
magnesian mineral, and labradorite and nephelite greatly predominate. 
It is proposed to call this variety rowvillite. Its mode, determined by 
calculation based on measurements by the Rosiwal (invariably spelled 
Rosiwald in the report) method is, plagioclase (Ab:An; to Ab;An,) 56 
per cent, nephelite 19.5 per cent, purplish augite 7.0 per cent, horn- 
blende 3.5 per cent, pyrite 2.5 per cent, apatite 1 per cent. The rock 
actually is a light-colored theralite, with a ratio of light minerals to dark 
of 85 to 15. 
