254 ' '^fi-'^ Afnerican Geologist. October, i899 
diclcd that "this gash was once an open fissure communicating with 
some reservoir of coal oil (petroleum) which still, it may be, lies 
beneath it undisturbed." Oil wells drilled during the past decade have 
fully verified this prediction, developing at a depth of 1,500 to 1,600 
feet and in close proximity to the grahamite fissure, a pool of oil 
which is but part of the prolific Cairo oil field. Hence the author con- 
cludes that there can be no doubt whatever that the fissure made by 
tension from the Burning Springs-Eureka uplift was filled with petro- 
leum from this pool, and that subsequently the oil was gradually con- 
verted by oxidation from infiltrating water into grahamite without 
any heat other than that afforded by the normal temperature of the 
earth. In this connection he cites Jeaney's experimental production 
of grahamite by passing heated air through petroleum for several 
hours. As a corollary from this conclusion, albertite, gilsonite, uinta- 
ite, and practically all forms of asphalt, including, as suggested by Dill- 
er. the "pitch" coal of Coos bay, Oregon, are oxidized petroleum, and 
the wonderful deposit of asphalt on the island of Trinidad is regarded 
as an old oil pool uncovered by erosion and hardened by volatiliza- 
tion and oxidation. w. o. c. 
A Contribution to the Study of Contact Mctainorphism. By J. 
Morgan Clements. (Am. Jour. Sci, 157, Si-gi.) 
This paper is essentially a detailed account of a somewhat normal 
instance of contact metamorphism not hitherto described. It occurs 
in the Lower Huronian iron-bearing formation of the Crystal Falls 
district of the upper peninsula of Michigan, where the Mansfield slate 
formation of the Michigamie Valley is cut by large and continuous 
masses of coarse doleryte (diabase). The intrusions show no evi- 
dence of endomorphic action and are not described; but the slate, 
which is an undoubted sedimentary deposit, exhibits, as we ap- 
proach the igneous contact, increasing metamorphism, and the suc- 
cessive phases known as phyllytes, spilosytes, desmosytes, and adinoles 
are observed in normal order. The least altered rocks, the normal clay 
slates, are found on microscopic examination to be of a semicrystalline 
character, containing, besides clastic quartz and original interstitial 
matter, secondary white mica, rutile, hematite, and actinolite. The 
phyllytes are similar, except that they are more lustrous, and the in- 
terstitial material has been changed to white mica. The spilosytes, 
desmosytes, and adinoles are the true contact products. They are 
dense, flinty, "hornstone-like" rocks, which show in some cases the 
fine banding of the original slates, while others are very characteristic- 
ally spotted. The mineralogical components are quartz, feldspar (al- 
bite), biotite, chlorite, white mica, actinolite. rutile, epidote, and iron 
oxide. In the first two varieties chlorite is the chief dark constituent 
with little or no actinolite, while the opposite relation holds for the 
adinoles. Complete analyses by George Steiger and H. N. Stokes are 
given for the normal clay slates, spilosytes, and adinoles. A compari- 
son of the analyses shows a marked increase of silica as the doleryte is 
approached, and a corresponding diminution of alumina and iron as 
