Intrusives of Lake 3IeiitpItre)iiago(/. — 3f((rsters. 37 
The uugite phenocrysts present the same characteristics as 
observed in the augite camptonite. It might be said in addi- 
tion that the zonal structure is somewhat more prominent, 
becoming intensified under cross nicols. The angle of ex- 
tinction varies from 20° to 24°. The augite of the second gen- 
eration which makes up the greater part of the ground mass 
is allotriomorphic, with a tendency at times to become idio- 
morphic. Scattered through the augitic magma are numer- 
ous but minute crystals of basaltic hornblende. The strong 
pleochroism from light yellow to deep reddish brown is espe- 
cially noticeable. With one or two excei)tions the hornblende 
may be said to show but one generation. A few very minute 
needles, however, were noted as inclusion in the augite phen- 
ocrysts. The remaining silicate is olivine, occurring either as 
partially decomposed granules, surrounded by rims of serpen- 
tine, or, occasionally as well developed phenocrysts exhibiting 
the usual crystalline form. Magnetite is very abundant and 
closely associated with the augitic groundmass. Consider- 
able glass was observed filling the minute interstices in the 
groundmass. 
Summary of Literature on Other Occurrences of 
MoNCHiQurrE, 
Such non-feldspathic rocks were first discovered b}^ Prof, 
Bonnet* in the Monchique mountains (Portugal) and subse- 
quently described by Leopold van Wervvekef as an abnormal 
limburgite. In 1887 Prof. E, O, Derby^ of the Brazilian Ge- 
ological Survey discovered similar eruptives in the region of 
Rio Janeiro. These, as in other instances, were associated 
with eleolite syenite. They were subsequently examined by 
Prof. RosenbuschJJ and in reality formed the basis for the 
determination of the new rock t^'pe, but received the name of 
the original locality discovered about 1S50. Along the shores 
of lake Champlain very similar dikes were found and subse- 
*AL(iAUVE Bonnet: Description ,i;('<)j4Tai)iii(iu(' el ^■eDloyiciiic di- ccltc 
lir(»\ iiicf. Ijisbon. IS.IO. 
f fv. V. Wehwekk: I'x'Kra^' /,ur Keiiiitiiiss dcr Liiiil)ui';L;ili'. Xcm-s .laiir- 
biicli, 187!), p. 481. Sec also Neucs .lalirbucli, 1880, vol. i. i)p. Ul-bSU. 
Uebor (lie N('|)hcliii syfiiltcn der Serra dc Moncliicpic iin siidliclicii 
Portuj^al uiid die dciisclbt'ii durchsolzi'iidcii (.Jostciiii'. 
:};0. A. Dkhhy: On Xcplicliiic Rocks in jira/il, I'li-. <^)iiail, .loiirn. 
Dcol. Soc. Ijondon, 1887, p. 457. 
i^M. Hunter and H. ItosKNUuscii: l^-bcr Monchiiniilc fin Cainplon- 
itischcs (ianjri'stein aiis dor Gefolgscbari dcr Klacolilli-syi'iiitf. Tsclicr- 
maks Mill, iind P.'lrojj. Milth., vol. xi, 1890, p. 44."). 
