No. 390.]} REVIEWS OF RECENT LITERATURE. 551 
The approximate composition of the rhyolite (I) and of the ande- 
site (II) is as follows: 
SiO2 AlO Fe0O0% FeO CaO MgO NaO K0 fen. -Tot 
E- 70.20 14090 53 sia 308.” 562 370 33I 2.50 = 100.54 
II. 66.85 14.08 3.06 409 of 380° 237 G07 = 98103 
Contact Phenomena in Michigan. — Between the graywackes, 
slates, etc., of the Mansfield formation, in the Crystal Falls district 
of Upper Michigan, and a mass of diabases on their flank, is a con- 
tact zone of dense hornstone-like rocks: that have been studied by 
Clements.’ As the intrusives are approached the graywackes and 
slates are changed into spilosites, desmosites, and finally adinoles. 
The unchanged clay-slates are banded rocks composed of quartz, 
muscovite, rutile, hematite, and an occasional needle of actinolite in 
a mass of feldspathic dust. With these are phyllites, which differ 
from the slates in being richer in muscovite, and in containing no 
feldspathic interstitial substance. The contact rocks consist of 
quartz, albite, biotite, chlorite, muscovite, actinolite, rutile, epidote, 
and iron oxides. The spilosites are mottled, the spots usually being 
- richer in chlorite than the surrounding matrix. In the few instances 
in which the spots are lighter colored, they are composed predomi- 
nantly of feldspar. The desmosites are like the spilosites, except 
that the spots are united into bands. In the adinoles actinolite is 
the chief colored constituent, while in the spilosites and desmosites 
chlorite plays this rôle. The chemical relationships existing between 
the unchanged and the altered rocks are shown by the following 
analyses (in addition to the constituents indicated below there are 
also indicated in the original small quantities of others) : 
SiOz TiO, Al0O3 FegO03; FeO CaO MgO KO NazO H:0 P2035 C 
Gone O9 2201 3:69 45 13 135 593 -S4 422 03 W 
M: ssr 1.90 3000 33i 9:19: 1.55 3290 70 672 350 f5 
III. 5777 .92 19.35 1.29 337 1-71 4.35 22 822 2.52 .04 
IV. 7416 37 1185 Ba TOG 310 %10 15 657. 57 -09 
I = slate, II = spilosite, III = spilosite, IV = adinole. 
Silica increases as the igneous rock is approached, and alumina 
and the iron oxides decrease. Moreover, the potassa, which is the 
predominant alkali in the unaltered slate, is replaced almost com- 
pletely by soda in the altered forms. The clay-slate is clearly 
clastic; the altered rocks are entirely crystallized. The former con- 
tains no albite, while the latter are rich in it. It appears that, in 
1 Amer. Journ. Sci., 1899, p. 81. 
