176 THE AMERICAN NATURALIST. [VOL XXXIIL 
- PETROGRAPHY. 
Marble. — Vogt! has given an abstract of the geology of marble 
deposits, together with an account of the structure and mechanical 
properties of the rock. He defines marbles as metamorphosed lime- 
stones in which complete crystallization has occurred, and divides 
them into regionally metamorphosed marbles and those produced by 
contact action. The latter are characterized by the presence of 
garnets, vesuvianite, scapolite, wollastonite, etc., and the former by 
the presence more particularly of quartz, grammatite, actinolite, and 
other hornblendes. Nearly all the marbles of commerce are dynam- 
ically metamorphosed rocks. The difference in microscopic structure 
between the two classes of marbles is illustrated by several figures 
representing thin sections, and the difference between calcite and 
dolomite marbles is illustrated by several other figures. Grains of 
dolomite are shown to interlock by much less complicated contours 
than those of calcite. The reasons for their variations in structure 
are discussed at some little length. The article is a thorough one 
in every respect and is well worth study. 
Grits Metamorphosed into Crystalline Schists. — Callaway? de- 
scribes the transformation of a series of grits and shales into what 
he regards as true crystalline schists. The phenomena were observed 
near Amlwch, North Anglesey. Grits, which in their original form 
are clearly clastic, have been changed by dynamic agencies into 
chlorite schists. ‘The quartz grains of the original rocks have been 
changed into areas of interlocking grains, and the matrix in which 
they were imbedded has been altered to a felt of chlorite, of mica, 
or a mixture of the two. In extreme cases the quartzes have been 
squeezed out into lenticules and bands of quartz mosaic, and between 
these have developed bands of chlorite and muscovite. 
and Cath- 
tein* give us very thorough accounts of the dioritic dikes and 
stocks at St. Lorenzen in the Pusterthal. The former describes the 
dike forms as diorite-porphyrites and norite-porphyrites. The diorite- 
porphyrites include quartz-mica-porphyrites, quartz-hornblende-por- 
1 Zeits. f. prakt. Geol. (1898), pp. 4 and 4 
2 Quart. Journ. Geol. Soc., vol. liv pose P- 374. 
8 Zeits. d. deutsch. geol. Ges., vol. 1 (1898), p. 1. 
4 Thid., p. 257. 
