Hawortu. | Physical Properties of the Tertiary. 255 
sc obscure in general character that one unfamiliar with them 
would not be able to make a corresponding distinction betweeu the 
gravels produced from them. 
The Sand.—The character of the sand is similar to that of the 
eravel. Itis much more largely composed of quartz, as sand usually 
is principally pure quartz. But perhaps it would be difficult to 
gather a handful of the sand anywhere in the whole Tertiary area 
of Kansas which did not show minute granules of feldspar and other 
constituents of the rocks of the mountainous areas to the west. 
The sand grains are generally rounded to a great extent implying 
long distances of travel. As regards degree of division the sands 
vary throughout almost the entire scale. On the one hand they 
gerade into the finer gravel with no line of demarcation between. 
On the other hand they reach the finest granules microscopic in 
dimension, and are so intermingled with the fine particles of the 
clay and silt that frequently one can hardly distinguish between 
them without washing the mass to get rid of the floating clay 
particles. The sand is sometimes quite well bedded when found in 
place, but often is almost structureless. Cross bedding is a common 
condition to observe, as is Shown in Plate XXX VIII taken from a 
bluff near Dodge City along the Arkansas river. 
Black Sand.—Almost everywhere over the Tertiary one fre- 
quently finds small accumulations of black sand which have been 
slightly segregated by the rainwater carrying away the finer ma- 
terials and leaving these little granules behind. They are com- 
posed almost entirely of grains of black oxide of iron, the greater 
portion of which are granules of magnetite, as can readily be shown 
by placing them within reach of a magnet. Usually about one 
third or one fourth of the volume will not be attracted by the mag- 
net, and are doubtless particles of dark colored hematite. These 
little granules are originally intimately mixed with the clay and the 
silt in the upper portions of the deposit so that they are entirely 
unobservable under ordinary conditions. But when the rains come 
the little rivulets of water on the hillsides carry the lighter and finer 
clay and silts away and wash the iron oxide grains into little streaks 
which lodge here and there in the rock or on the hillside or are 
spread out in the fields and attract attention. Unfortunately the 
