382 REVIEWS 
the basin, the occurrence of marsh-formed or land-formed lignites in 
similar situations, the interstratification of beds of gypsum or other 
desiccation products, and analogous criteria that imply aérial con- 
ditions. Trere 
The Crystal Falls Iron- Bearing District of Michigan. By J. Morcan 
CLEMENTS and Henry Lioyp Smyru, with a chapter on the 
Sturgeon River Tongue by William Shirley Bayley and an 
Introduction by Charles Richard Van Hise. U.S. Geolog- 
ical Survey. Monograph XXXVI. Washington, 1899. 
This report is the third in a series of four monographs on the iron- 
bearing district of the Lake Superior Region. Two having been 
published previously: one on the Penokee district (Monograph XIX). 
The other on the Marquette district (Monograph XXVIII). The 
fourth, on the Menominee district, is to follow. 
The Crystal Falls district was divided areally, the western half being 
studied by Mr. Clements and the eastern half by Mr. Smyth, and the 
Sturgeon River Tongue by Mr. Bayley. The investigation was con- 
ducted under the charge of Mr. Van Hise, who sums up the general 
results in an introductory chapter. ‘The district embraces 840 square 
miles. As pointed out in the introduction the rocks belong to the 
Archean and Algonkian. The latter consisting of a Lower Huronian 
and an Upper Huronian separated by unconformity. The Archean is 
believed to be wholly igneous in origin, it occupies a broad area in the 
eastern part of the district and has not been closely investigated. 
Several smaller areas occur within parts of the region carefully studied. 
Owing to the readily decomposable nature of the rocks in places and 
to the drift mantle the detail character of the formations is unknown 
for part of the area described by Clements, and in the belt worked by 
Smyth the rock surface is almost wholly concealed by glacial deposits 
and vegetation. It will be seen under what adverse circumstances the 
field work was carried forward, and how much credit is due the geol- 
ogists who have brought to light so much valuable information from 
so unpromising a region. 
The Lower Huronian consists of quartzite, dolomite, slate, a volcanic 
formation, and some schists. ‘The series has a minimum thickness of 
2200, and a possible maximum thickness of 16000 feet. The sediments 
probably nowhere exceed 5000 feet in thickness. ‘The Upper Huronian 
