Fence Wall Gcologtj. — t'oerste. 8G7 
studied southern Arkansas and Texas, but also on professor 
John C. Branner, the state geologist. The State of Arkansas 
must be complimented to have secured the services of such 
able observers. 
Cavibrichfe^ Mass., September. 18S9, 
FENCE WALL GEOLOGY. 
By Aug. F. Foerste. 
In drift covered areas actual exposures of bed rocks are often 
insufficient in number to determine even the simpler problems 
of geology. In such cases any assistance derived from other 
sources is often of value. In regions where the drift near its 
surface contains boulders sufficient in size and abundance 
for the construction of fence walls, these boulders will often 
furnish the desired data. Since such boulders are placed in 
fence walls as a rule in the most expeditious manner consistent 
with the clearing of the adjoining fields, they have usually 
been removed too short a distance from their position in the 
fields to seriously affect any investigation as to their distribu- 
tion. Moreover, an examination of the neighboring topogra- 
phy, the slope of the lands, the presence of streams and ponds, 
and similar data, will frequently even make their original 
position in the fields quite certain. The existence of fence 
walls also implies the existence of boulders in sufficient num- 
bers and of sufficient size to insure the observer that their orig- 
inal location, while a part of the bed rock, is not too far distant 
to make a study of their distribution profitable. The study of 
fence walls, therefore, becomes the study of the larger ele- 
ments of the drift. 
It is well known that near their source in the bed rocks the 
elements of the glacial drift are quite angular, but that owing 
to attrition the corners and edges are gradually blunted or 
worn off as their distance from the source increases, until 
finally the fragments become quite decidedly rounded. All 
this is of course accompanied by decrease in size. With a fur- 
ther increase of the distance from the original source the size 
of the boulders becomes too small even for use in fence walls, 
and the further increase of distance is therefore also noticed 
by the smaller percentage of such boulders found in the fence 
walls. This smaller percentage may also be due to another 
