Personal and Scientific Nvws. 265 
•artesian waters of the Dakotas. There was first described a detailed 
section which had been carefully measured from the base of the Potsdam 
to the White River Miocene formation, along a line passing through 
Rapid City to the Bad lands. The thicknesses of the upper Cretaceous 
members in this section have since been most satisfactory verified by 
the deep-well boring on the Rosebud Indian reservation. The salient 
features of the general stratigraphy were pointed out and the alleged 
unconformities in the Juratrias formations were discussed. Attention 
was called to a well defined peneplain now represented by the eastern 
" hog back " foot hills of which the very even crest lines are at an alti- 
tude very nearly 4,000 feet above sea level for over 100 miles. Diagrams 
were exhibited of an interesting laccolite west of Tilford and the struc- 
ture of the Bear Butte and Warren Peaks eruptive areas were described. 
Some incidental observations in the nucleal region of the Hills brought 
to light some important details of stratigraphy of the Algonkian beds, 
and some examples illustrating the development of schistosity in the 
vicinity both of granitic and younger eruptives. 
In the discussion which followed this paper, Mr. M. R. Campbell 
alluded to the ciose similarity between the relations of the even crest 
lines of the "hog back" ranges described by Mr. Darton. and the 
Appalachian ridges, and endorsed the view that they are similarly the 
remnants of peneplains preserved by the harder rocks. 
Mit. F. W. Crosby presented a paper entitled " The sea mills of 
Cephalonia." These mills are run by sea water which flows into fissures 
with considerable velocity. The origin of these fissures and the condi- 
tions which enabled the sea water to sink into them below the level of 
the sea have been the subjects of popular speculation for many years, 
but they appear to have atracted but little attention among geologists. 
Mr. Crosby then quoted a paper by his son. Prof. W. O. Crosby, in 
which the mechanism of the phenomena was discussed and a hypothesis 
offered to account for it. 
A paper on the "Stratigraphy at Slate Springs, California" was 
read by Mr. Lindgren. 
At the 45th meeting of this society held on March 11, Prest. 
S. F. Emmons, in the chair, two papers were read, one by Mr. 
Bailey Willis on ''Evidences of Ancient Shores,'* and the 
other by Mr. David W t hite on the " Thickness and Equiva- 
lence of some Basal Coal Measures Sections along the Eastern 
Margin of the Appalachian Basin." 
Mr. Willis discussed the evidences of ancient shores with reference 
to their position, trend, and duration. Five classes of evidence were 
enumerated : namely. (1) overlap or unconformity. (2) suneracks, trails, 
or ripple-markp, (3) coarser deposits, (4) thicker deposits, and (5) syn- 
c-lines of deposition. 
Any point on an unconformity marks with precision a point on sonic 
shore line at some instant of lime, bul as the outcrop of an unconform- 
ity cannot be assumed to be parallel to the former shore line, this evi- 
dence does hot define the trend of the ancient shore, and as the shore 
was in transit ii° duration was transient. 
In contrast with this c mclusion was placed that derived from thick 
deposits of shales, such as are formed by the delivery of a large volume 
of sediment concentrated at the mouth of a river draining an extensive 
watershed. These conditions result in the accumulation of a Lenticular 
formation which thickens rapidly from the shore and thins more gradu- 
ally seaward. When the thickness of the shale is pronounced, tin' du- 
ration of the conditions was probably lone- continued. Such evidence 
therefore indicates the approximate position, general trend, and long 
duration of the ancient shore. 
