PIATT COUNTY. 195 



width. The. total area of timbered land in the county probably does 

 not exceed 50 square miles. 



The prairies are bordered with a growth of laurel oak. pin oak, hick- 

 ory, cherry, plum and crab apple, with sometimes bur oak and black 

 walnut. Between the prairies and the Sangamon bluffs we found white 

 oak, sassafras, shellbark' hickory, black oak and hazel ; on the sloping 

 bluffs, white oak, black oak, service berry, irpn wood, black haw, red 

 tree, sugar tree, linden, ash, red oak, walnut, red elm and poison oak. 

 Good timber abounds on the bottoms, including black walnut, bur oak, 

 ash, maple, hickory, honey locust, hackberry, mulberry, red oak, linden, 

 sycamore, and a few blue ash trees were observed. 



Away from the streams the country is either flat or very gently undu- 

 lating, rising by easy ascent to the upland prairie and gradually blend- 

 ing into the higher mound-like elevations. 



8tr atlgr aphical Geology. 



~So formations, older than the Drift, appear in this county. 



The character of the alluvium is similar to that of the adjoining coun- 

 ties and it includes the soil and recent deposits along the streams. 



Drift. — At the bridge on Sangamon river, near Monticello, it is thus 

 exposed : 



Ft. 



1. Yellowish-brown clay 5 



2. Clay, sand and bowlders 5 



3. Dark ash brown clay, fine sand and a few pebbles 4 



4. Black clay 1 



5. Clay streaked, black and dark brown with ochrey red 8 



On Sangamon bluffs, four miles below Monticello, there is exposed : 



Ft. 



1. Brown clay 6 



2. Pebbles and clay 10 



3. At top dark brown clay, below reddish-brown finely comminuted sand and clay 14 



Between Monticello and Centre ville the road washings disclose three 

 to four feet of bright brown clay, sometimes brown sand, pebbles and 

 bowlders. 



On the prairies there are bowlders of granite of various colors, gener- 

 ally gray, red and grey sienite and sienitic granite, quartzite and 

 altered sandstone, gneiss and greenstone ; and in the altered drift we 

 found Devonian fossils and fragments of Coal Measure rocks. 



Springs highly colored with oxyd of iron are often found issuing from 

 the drift sands. On Willow Branch, in sec. 29, T. 19 K, B. 5 B., there 

 are many such springs, some of them strongly chalybeate. In one of 

 them gas arises and a quantity of brown sediment is deposited on its 

 sides ; the ground in front is very marshy for the space of two acres. 



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