Inlriisives of Luke JlcDip/iromif/o;/. — Mars/cys. 33 
fact it is thought best to regard this coin bi nation as (iinjile 
cdmpt unite. 
No. 20. Of the typical camptonites but one occurrence was 
found, (No. 20). In this dike the basaltic hornblende in two 
generations is tlie only colored silicate present. Magnetite is 
very abundant. The amount of plagioclase present is not 
large, but it is quite fresh. Considerable glass was also de- 
tected in the groundmass. Comparing this section with the 
original camptonite* discovered by Hawes, the only difference 
to be noted is that the hornblende is not so well developed in 
the dikes from lake Memphremagog. Although they are 
much smaller the idiomorphic habit is quite apparent and 
other petrographical characteristics of this type are very easily 
recognized. 
AiKjite camptonite. — Of all the dikes belonging to the camp- 
tonite series the augitic type is by far the most abundant. 
In addition to this hornblende in two generations, we find 
augite in the same relationship. In many cases the augite 
is far more abundant than the hornblende. The idiomorphic 
habit of the hornblende is retained as in the camptonite 
proper. The augite phenocrysts are well developed. The 
zrmal phases so prominent in the Lake Champlainf dikes are 
equally conspicuous in the dikes under consideration, the 
central portion of the individual being in general very light 
yellow while the peripheral area shades into light pink which 
brightens as the edge is approached, the latter being some- 
what pleochroic. Occasionally the central part is bright green 
surrounding a narrow rim, light yellow in color. It has been 
noted that with increase in the intensity of color in the pe- 
ripheral area there is a corresponding increase in the extinction 
angle. The variations noted reach a mamimum of 8". 
The augite of the second generation shows definite crys- 
talline form. It is packed in between the feldspars and is the 
only granular constituent present. Pleochroism is noticeable. 
Small olivines with characteristic form and decomposition 
*Thr Jiuthor vvislies to ackuowlt'dfic the aiil so kiiull\' rciulcrt'd by 
Prof. J. F. Kemp, of Columbia ('ollcgp, N. V., in ioaiiiii",' tiiin sec- 
tions of camptonite from tiu' original locality of Ilawes, and oU'ering 
sufjfrestions wliicli have been very helpful in the study of these intru- 
sives. 
fSee Bull. U. S. Geol. Survey, No. 107, p. 30. 
