202 The America it (ieoUxjint. September, 1895 
CORRESPONDENCE. 
Rfx'Ext CiEOLocJitAL WoiiK IN Soi'TH Dakota. By the direction of 
the State Board of Regents of Education the School of Mines of South 
Dakota sent two parties into the field in May and June of this year. 
The general oversight of the work was placed in the hands of the 
state geologist. One party, consisting of Prof. F. C. Smith of the 
School of Mines and several of his students, spent the time in carefully 
examining the section of the Black hills along Rapid creek, with the 
special purpose of unravelling the complicated structure of the Algon- 
kian slates and quartzite. The other party, consisting of myself and 
one assistant, made an extended reconnoissance of the northwestern 
portion of the state. The following points of general interest to geolo- 
gists were ascertained and it is thought best to place them on record 
before thepreparation of a more careful report. 
1. Numerous small bivalve shells have been found in the Purple lime- 
stone which lies in the Red beds and which has l)een reported by all. 
previous observers as entirely withovit fossils. 
2. Numerous folds of great extent and of very complex character are 
found to occur in the slates along Rapid creek in the eastern portion 
of the Black hills. Also an important advance in the tracing of the ex- 
tent and subdivisions of the Algonkian. 
.3. Miocene beds, both White River and Loup Fork, with character- 
istic fossils, have been fovmd overlying wide areas of the Laramie north 
of the Black hills, covering quite deeply most of Harding county, with 
thin outliers over the north half of Butte county and south half of Ew- 
ing. In the Short Pine hills and Slim buttes these deposits exhibit a 
depth of 200 to -40,0 feet with characteristic fossil features closely resem- 
bling those of the White River region. 
4. An area of disturl)ance was fovind in the north half of Slim buttes 
in northeast Harding county covering perhaps 20 to 25 square miles. 
This consists of sharp folds, including the Laramie and White River 
beds, with throws of perhaps 100 feet and dips of 25 degrees. 
5. Upon these beds lie horizontal strata of white sandstone over 100 
feet in thickness, doubtless of the Loup Fork age. Photographs of in- 
structive exposures were secured. 
6. The lignite beds of the Laramie of North Dakota and Wyoming 
are found to extend so as to underlie most of Ewing, Harding and Mar- 
tin counties. These featvu-es are quite constant in thickness over wide 
areas, especially toward the north. Two of them, four to five feet in 
thickness, underlie the Cave hills, and the lower one extends scores of 
miles und&r the surrounding country. In some places, as in the north 
half of Slim buttes, three beds were found, five, six and ten feet in 
thickness, in a vertical distance of 50 or 60 feet. With these great 
quantities of fossiliferous clays, atfording beautiful specimens of fossil 
leaves, were found. J. E. Todd. 
V^ennillioa, S. D., Aii/j. ■'>, 1<S!>.'). 
