SOURCES OF INFORMATION AS TO THIS REGION. 207 
a“ 
of the workings on the gray sandstone of the Upper Division of the series, 
at the Nonesuch mine, in the Porcupine Mountains, there are no mining 
operations to assist in a detailed study. Foster and Whitney’s brief ac- 
count of the region between the Ontonagon and the Montreal rivers,! a 
short account of the Porcupine Mountains, by Col. Chas. Whittlesey,’ and 
an equally brief description, by the same geologist, of the region between 
the Montreal and Bad rivers,’ embody all the information obtainable 
previous to my own acquaintance with this district. 
In the summers of 1873, 1876 and 1877 I made examinations of the 
regions drained by the Montreal and Bad rivers, and the results were pub- 
lished in 180 in the Geology of Wisconsin.* In the same volume appears 
an account by Professor Pumpelly of the microscopic characters of a num- 
ber of the specimens collected by me in this region. In addition to what 
is given in the above-named publications I have to base the following de- 
scriptions upon the results of a detailed examination of the Porcupine 
Mountains, by my assistants, Messrs. W. M. Chauvenet, A. C. Campbell, B. 
N. White and R. McKinlay, of a cursory examination by myself of the 
rocks in the vicinity of the Ontonagon, and of my own detailed micro- 
scopic study of all specimens gathered. 
The conditions already described as obtaining at the crossing of the 
Ontonagon remain the same all the way to the Montreal River, so far as 
general stratigraphy and kinds of rocks are concerned, save that there is a 
very considerable expansion downwards, due chiefly to the appearance at 
the surface of layers which farther east are buried beneath the Eastern 
Sandstone. There are, however, noteworthy changes in structural features, 
in the courses of the rock belts, and in the width of country occupied by 
them. Save in the Porcupine Mountains, which lie to the north of the 
Main Trap Range, the usual northern dip everywhere prevails, but, after 
two townships are crossed west from the Ontonagon, it has flattened enough 
to increase. very materially the width of country occupied by the Lower 
Division of the series. The rising from beneath the Eastern Sandstone of 
1Op. cit., pp. 74-80, 1850. 
2 Engineering and Mining Journal, Vol. 23, p. 254, April 21, 1877. 
3Proc. Boston Soc. Nat. Hist., July, 1863; also Geology of Wisconsin, Vol. III, Part III, Ap- 
pendix A, pp. 216-223. 
4Geology of Wisconsin, Vol. III, Parts I and III. 
