OF ARKANSAS. 



121 



escarpment on the north bank of the Barren fork, extending clown to the 

 bed of that stream. 



The different beds and their order of superposition, from the schistose 

 sandstone of College hill, to the cherty limestone of the Barren fork of the 

 Illinois river, are shown in the annexed section. 



i i i 



i i i i 



i i i i 



L I 



fa 



45 



CL | CL 



CL 



CL CL 



CL 



I 



CL | CL 



CL 



CL CL 



15? 



40 

 to 

 60 



Schistose sandstones of College hill. 



Archimedes limestone over the Boonsboro 

 spring. 



A modification is ob- 

 servable in this section, 

 causing it to differ from 

 those sections previously 

 given of the strata under 

 the Archimedes lime- 

 stone : it consists in the 

 introduction of the build- 

 ing-stone amongst the 

 underlying shales. Near 

 the Barren fork, the 

 strata have a strong clip, 

 9 to 13 deg. north north- 

 east and north-east. 

 The fossiliferous lime- 

 stone lies in a pavement 

 form, with a regular and 

 deeply marked system of 

 joints, having a course 

 north-west and south- 

 east. The most abund- 

 ant fossils in this rock are 

 Terebratula piano- sulc at <( 

 and planum-bona ; Pi •<>- 

 ductus cora and a Pro- 

 ductus allied to P. semi- 

 reticulatus ; a favosite re- 

 sembling the basaltica, but so deeply imbedded and firmly attached in the 

 substance of the rock that they could not be properly examined in place, 

 nor detached without defacing them in such a manner that the disposition 

 of the rows of connecting pores could not be seen so as to determine their 

 specific character. 



Both Productus cora and Terebratula plano-sulcata were found, also, in 

 the overlying chert. 



This limestone has marly and shaly partings. 



Dark shales, 10 to 15 feet in thickness. 



Freestone or building-stone. 



Shale. 



Chert. 



Fossiliferous limestone. 



Sandstone. 



Chert and cherty limestones of the Barren 

 fork of the Illinois River. 



Black shale ? 



