The Late Minnesota Survey. — Winchell. 251 
These belts of intensest metamorphism, whether productive 
of granite or of gabbro, have a parallelism with each other, and 
with the northwestern rim of the great synclinorium of the 
basin of lake Superior, marking successive continental folds, 
in harmony with a system which continued through Archean 
and Taconic time, and even into the Upper Cambrian. 
(12). In the progress of the survey the mineralogy of the 
state was considerably extended, there having been added fifty- 
six species to the known minerals of the state. The greater 
part of these were identified in the region of the crystalline 
rocks. 
Of the economic and educational results the following are 
worthy of mention : 
(i.) In the settlement of the prairie regions of Minnesota, 
which are based largely on a uniform but very thick deposit 
of drift clay, the immigrant usually depended for domestic 
water supply on shallow wells, not usually over thenty-five 
feet in depth. In some of these wells^ a sufficient supply of 
good water was found in thin gravel or sand layers ; but in by 
far the larger number the supply was scant. Such scant supply 
was derived by seepage from the till. Had it not become con- 
taminated by artificial causes it would have been sufficient. 
But, in the absence of stone and brick for walling up their wells 
the settlers frequently resorted to pine planks which they ob- 
tained from the lumber markets. These they set vertically so 
as tO' enclose the well reservoir completely. Typhoid fever and 
enteric disorders became abnormally frequent and fatal, so 
much so that capitalists who were interested in the settlement 
of the lands of the state were fearful that the foulness of the 
usual well water would effectually retard the development of 
the agricultural lands. The health officers of the state shared 
in this suppressed alarm. 
After a careful examination of the conditions it was dis- 
covered that the difficulty arose almost solely from the use of 
pine planking in curbing the new wells. The prevailing alka- 
line quality of the water seemed to hasten the decay of the pitch 
oi the pine, and, uniting with the resultant acids, not only pro- 
duced offensive odors but favored the propagation of those 
germs that are formed in stagnant water. The waters were 
found to be wholesome when fresh from the earth, although 
