142 Tlie Amaican Geologist. Marcii, istw 
and associated compounds. The argillaceous shale at the 
base of the exposed colunm is greenish gray in color. The 
sand present in it occurs in small, irregularly distributed areas, 
giving a mottled appearance to the hand specimens. Some 
of these sand patches have a regular outline that may indicate 
organic association. Linguloid fragments are rare. A mica- 
ceous mineral in small scales is accessory. 
Chapter II. Litliology of tJic Igneous Rocks. 
Several descriptions of these rocks have been published* 
and the lithologic character of the typical species is so well 
known as to require no further attention than the following 
Ijrief paragraph as a summary. The rock varies from yellow- 
ish green to greenish black in color. It is often porphyritic 
and frequently amygdaloidal and pseudo-amygdaloidal . Usu- 
ally it is rather finely crystalline and nearly always very much 
altered from its original mineral composition. Lustre-mot- 
tling is common. Microscopic examination reveals the con- 
nection between this lustre mottling and the ophitic structure 
represented by the intergrowth of augite and plagioclase. Be- 
sides these two minerals, magnetite and pyrite occur as pri- 
mary constitutents. The secondary constitutents are quartz, 
chlorite, epidote, apatite, calcite and a grayish white granular 
substance whose identity is undetermined. 
This rock has been called a melaphyr by Pumpelly, a 
melaphyr porphyry by Kloos and Streng. trap by Winchell, 
porphyritic trap by Owen, a diabase also by Kloos and Streng, 
and an epidote diabase amygdaloid by Pumpelly. Kloos and 
Streng call this rock melaphyr porphry, but point out that 
olivine and an amorphous matrix are wholly wanting, while 
both the essential constitutents and the alteration products 
common' among diabase are present; and the conclusion is 
*Owen: Geol. Survey of Wis., Iowa and Minn., 1852, p. 164. 
Kloos: Zeitschrift d. Deutsch. Geol. Gesells., 1871, p. 417. Trans, 
by Winchell: loth Ann. Rept. Minn. Geol. and Nat. Hist. Survey. 
1881, p. 175. 
Kloos and Streng: Neues Jahrbuch fur Min. Geol. und Paleont., 
1877, p. 31. Trans, by Winchell: nth Ann. Rept. Minn. Geol. and 
Nat. Hist. Survey, 1882, p. 30. 
Kloos: Zeitschrift d. Gesells. fiir Erdkunde zu Berlin, Bd. XII, 
1877. Trans, by Winchell: 19th Ann. Rept. Minn. Geol. and Nat. Hist. 
Survey, 1890, p. 81. 
Chamberlin (Strong): Geol. Wis., vol III, 1880, pp. 365-4^8. 
