Geology of Southeastern Iowa. — Gordon. 239 
gives 939 feet which still seems short of the actual thickness 
of the series. 
At Sigourney the drillers give 609 feet of sandstone but it is 
altogether probable it is the same as the others. At Keokuk 
the current of water was so strong that samples were not 
easily obtained, but at different times samples were secured, 
showing a brownish shaly limestone above sometimes white 
and fine-grained alternating with sandstone which was hard 
and calcareous in portions. Thickness of each division could 
not be made out. The lower part seemed to be cavernous, the 
drill dropping two feet at one point. The flow of water was 
increased at two places which doubtless represents the num- 
ber of sandstones included. At Ottumwa the rock showed 
substantially the same characters. Mr. Hamilton says that 
the last 697 feet was "hard limestone full of holes, the sides of 
which are encrusted with a white substance evidently deposited 
by water. A piece of this rock about twice the size of a man's 
fist was brought up from a depth of about 1,700 feet having 
been caught in some way in the rope above the drill." It 
seems conclusive that the Lower Magnesian series has a much 
greater thickness in Iowa than has heretofore been supposed. 
As the Davenport well ^ shows 622 feet of this series, which is 
corroborated by the records above with an increase in thick- 
ness, the conclusion seems justified that the maximum thick- 
ness of this formation within the limits of Iowa can not be 
less than 1,000 feet. In the vicinity of St. Louis, Mo., it is 
nearly 2,000 feet in thickness.' 
There is some probability that the Hubinger No. 3 now well 
under way will be continued through the Lower Magnesian 
series in the hope of finding more water in the Potsdam. It is 
greatly to be hoped this will be done as it will definitely settle 
the question of the thicknes of this series in Iowa. 
A POCKET MAPPING INSTRUMENT. 
By Alfred C. Lane. 
What with compass, notebook and pencil, one hammer or 
possibly two, map, lunch and collecting bag and perhaps 
barometer, the field geologist is apt to realize too forcibly the 
meaning of the Latin term "impedimenta." The little instru- 
^ American Geologist, Feb. 1889. 
^ Missouri Report. 
