Apparent Anomalies of the Postville Well. — Calvin. 199 
a thickness of about sixty feet. The drillings obtained showed 
the material to have the same color and chemical composition 
as the argillaceous and calcareous shales making up the “basal 
shales’ 7 No. 1. and the “green shales” or No. 3 of the preced¬ 
ing section. At 512 feet from the surface the samples proved 
that the drill had again entered the Saint Peter sandstone. 
Drilling proceeded to a depth of 515 feet and then stopped, the 
supply of water being sufficient for the purpose for which the 
well was made. That the clear quartz sand taken at depths 
of 512 and 515 feet from the surface belonged to the stage of 
the Saint Peter sandstone was not, in this instance, disputed. 
If the sandstone between 135 feet and 450 feet from the 
surface does not belong to the Saint Peter stage then a num¬ 
ber of serious difficulties present themselves. First, the facts 
would have to be interpreted as indicating a bed of sandstone 
interstratified with the Trenton, but field observations have 
never shown any arenaceous beds between the top of the Saint 
Peter and the base of Galena. The Saint Peter sandstone ends 
abruptly and the lower Trenton shale begins without any in¬ 
termingling of characteristics belonging to the two forma¬ 
tions. There are no transition beds in the lower part of the 
Trenton and there are no known sandstone layers at any ho¬ 
rizon within the limits of the Trenton series. Second, the 
facts would indicate that the Trenton shales and limestones 
have a thickness of more Than 425 feet, a thickness wholly in¬ 
consistent with any observations made in the field. A thick¬ 
ness of 350 feet is so far in excess of measurements published 
by the earlier observers as, at first, to justify serious doubt 
respecting the reliability of the data on which it rests. Ob¬ 
servations were repeated more than once before it was con¬ 
sidered safe to publish the figures given in the report on 
Allamakee county, and that report, while making the total 
thickness of the Trenton 100 feet greater than the dimensions 
given by any previous publication, did not give the full meas¬ 
urements atforded b}^ the several members of the section where 
they attain their maximum development. Third, the assump¬ 
tion that the arenaceous layer reached at 435 feet is not 
Saint Peter is inconsistent with field observations in another 
particular. The Saint Peter sandstone is exposed in the val¬ 
ley of the North fork of the Yellow river about eight miles 
