OF ARKANSAS. \ 33 



with some intercalated beds of limestone. The top of this marly shale is 

 230 feet below the summit. It is at least 100 feet in thickness, down to 

 the junction of this shale and an underlying bed of limestone. 



The rocks are evidently much disturbed in this mountain. At one point 

 in the descent, a dip of 4 deg. south-west was observed ; but a short 

 distance further the dip was reversed. 



CRAWFORD COUNTY. 



Close to the spring, at the foot of the mountain over which we passed 

 from the Barren fork of the Illinois to Lee's creek, the Archimedes lime- 

 stone is in place, 260 feet below the level of the principal mass of corre- 

 sponding limestone, in the section of the north-west slope of the mountain. 



There is no doubt a dislocation of the whole of the rocks of the moun- 

 tain with a subsidence to the south-east, which causes so sudden a depres- 

 sion of this limestone. 



Associated with Archimedes at the spring, near the foot of the mountain, 

 on Lee's creek, occurs Agassizoerinus conicus. 



Lee's creek meanders for many miles at the base of high cliffs and 

 slopes of the spurs of the Boston mountain range, which are composed of 

 sandstones, shales, and limestone, belonging to the age of the millstone 

 grit and subcarboniferous group, the strata gradually dipping down stream 

 towards the south. No coal has ever yet been discovered on this part of 

 Lee's creek, but near its head, 15 miles above Alfred Smith's place, a bed 

 is represented as occurring, and ranging from 10 to 12 inches in thickness. 



Half a mile below Alfred Smith's farm, sandstone was observed dipping 

 10 deg. to the south-east, the Archimedes limestone being no longer visible 

 above the bed of Lee's creek. 



One of the most remarkable features in the scenery of north-western 

 Arkansas is the " Natural Dam," represented in the steel plate engraving 

 forming the frontispiece to this volume. It is formed by a solid bed of 

 sandstone, from 6 to 8 feet in thickness, which runs entirely across the 

 bed of Lee's creek, forming a natural barrier to the descent of the water, 

 in consequence of the gradual dip of the rock up stream towards the north- 

 east, at an angle of 4 to 5 deg. being just the proper inclination to 

 dam the water back, and throw it to a sluice, that might be solidly and 

 permanently fixed to this rock wall near where it runs into the north-west 

 bank. 



The log mill, seen in the frontispiece, is one of the rudest description ; 



