90 The American Geologist. February. i904. 
Silurian age, which was found near the Chicago, Milwaukee 
& St. Paul R. R. where it crosses the northern boundary of 
Lincoln county. The striae extend more or less discontinued 
over the entire smoothened surface of the bowlder. They are 
not decidedly parallel to each other, but are more or less in- 
clined toward each other, while their depth varies from ^/^ to 
Vio of an inch and their breadth from i to 3 mm. A list, pre- 
pared from collections from several localities, will show their 
character and may suffice to prove the decidedly northern or- 
igin of these erratics, of which many can be traced with a 
greater or less degree of certainty back to the mountainous 
regions of Minnesota and possibly farther. 
From the northern ridge : 
I . Reddish porphyritic granite, 3x4 feet ; 2. dark gneiss ; 
3. a pinkish quartzyte ; 4. almost black hornblende schist; 5. 
gray fine and medium grained granite, the gray being in some 
cases replaced by a yellowish shade, while the iron pyrite is 
very conspicuous ; 6. crystalline, light yellowish limestone of 
probably Silurian age, showing impressions of Bryozoa. 
From the vicinity of Lennox were obtained bowlders of: 
I. A mica-dioryte, porphyritic; 2. yellowish medium grained 
granite, abounding in mica ; 3. a light coarse grained granite : 
4. a reddish small grained granite ; 5. a bluish gray medium 
grained gneiss ; 6. a crystalline, yellowish gray limestone. 
On top of the bluffs of the Big Sioux near Spring creek the 
following bowlders may be noted : 
I. Coarse grained feldspatic granite of a pinkish hue; 2. 
medium grained granite of nearly the same color ; 3. a very firm 
dark gray gneiss ; 4. a light-colored, at places yellowish, firm 
limestone, showing traces of striation and spicules of sponges 
and graptolites; 5. a porphyritic dioryte of dark color. 
On the drumlms on Long creek have been observed : i . 
pinkish and gray coarse and fine grained granites. 2. a medium 
grained quartzyte and quartz-schist of grayish color as well as 
of pink shades ; 3. a chocolate gneiss ; 4. a gray, coarse grained 
gneiss, showing a jointed structure, 5x3 feet; 5. the red Sioux 
quartzyte ; 6. a gray syenyte with smooth surface, speckled 
black by hornblende; 7. a light yellow (Silurian) limestone of 
firm texture, 5x4 feet. 
