Review of Recent Geological Literature. 197 
No. 42, 182) H. A. Miers describes this apparently new mineral which 
was observed on specimens ofargentite from Chanarcillo. To the naked 
eye this mineral appeared to be gothite, the microscope, however, re- 
vealing its true character, which must be referred to another mineral. 
No quantitative examination was made on account of the small quantity 
of material ; a qualitative analysis, however, showed the presence of 
silver, arsenic and sulphur. The physical characters as a whole, prevent 
the mineral from being referred to proustite or xanthoconite, the mineral 
being nearer like the former in its physical characters. The specific 
gravity and hardness have not been determined. 
Report of exploration of the glacial lake Agassiz in Manitoba, by 
Warren Upiiam. ( Part E Annual Report, vol. iv, 1888-9, Geol. and 
Nat. Hist. Sur. of Canada.) pp. 156, Montreal, 1890. 
In this report Mr. Upham has given a more detailed and comprehen- 
sive account of lake Agassiz than in any earlier report. The first 
accounts are found in the reports of the Minnesota survey. A bulletin 
of the United States geological survey adds much to the available 
literature of this lake, and occasional references to it elsewhere have 
made lake Agassiz a familiar term to the student of pleistocene geology. 
This report comprises that portion of lake Agassiz in Manitoba which is 
an the prairie region, but the lake included a large area further east and 
indefinitely northward which has not yet been examined and which, 
from the nature of the country, it is difficult or nearly impossible to 
survey at the present time. Much of this unsurveyed region is wooded 
and rocky, and it is nearly without human habitation. To trace the 
beach lines would be difficult and expensive. 
Considering the great amount of information, however, which Mr. 
Upham has now given concerning the nature and the probable cause of 
this lake it is not so regrettable that the eastern part cannot be re- 
ported on. 
Mr. Upham has availed himself of every avenue of approach to a 
solution of the problems involved. Adding to a minute study of the 
•drift-sheet itself both in Dakota and in Manitoba, a mass of definite 
■data from railroad levels, he proceeds to the study of common wells and 
the molluscan fauna which some of them have brought to light. He 
gives a " history of lake Agassiz," a description of the topography of the 
basin, its beaches, deltas and its occasional osars, and attributes the 
existence of the lake, with its north and eastward ascending beach lines, 
to a depression of the crust of the earth in that direction united with 
the cotemporary prevalence of a great ice-sheet which, moving from 
the northeastward formed a barrier against the water that gathered at 
its southern margin and compelled it to seek the lowest southward way 
of escape. 
The names of the upper beaches are derived from points in Minnesota 
where they were first observed; but it is found that cadi of these 
beaches becomes divided into two or three, further north, having slightly 
