52 IOWA ACADEMY OF SCIENCKS. 



THE GEOLOGY OF CROWLEY'S RIDGE, ARKANSAS. 



BY PROF. R. ELLSWORTH CALL. 



'.A/tstract.) 



( *rowloy's Rido-e is si low ranoe of hills fonnino- tht" only 

 conspicuous feature in the topoiiraphy of Northeastern Arkan- 

 sas, and extends in a «'eneral nortli and south direction from 

 the Missouri state line to the ( ity of Helena, where it ends 

 al)ruptly. The total lenoth is therefore about 145 miles. It 

 is a rano-e of hills of varyin<>- width, its averao-e beino- Ml)out 

 four to six miles. The elevation is, on the average, from 1 75 

 to 250 feet above the surrounding- country. The «-en(n'al sui'- 

 face is very irreo-ular and presents a line example of quaqua- 

 versal erosion, the heads of the numerous ravines often 

 departino- from the same point. 



The aofe of the rid,o-e is a mattei- of some (juestion for it 

 is largely made up of deposits that are believed to ])e of the 

 ag-e of the Orange Sand deposits. That the age of these 

 sands is yet in dis[)ute results from tiie fact that their mode 

 of origin is not well understood, and ])esides they differ so 

 widely tit many j)oints of their distribution. It has, however, 

 been assumetl in these notes that they are ])roperly to ])e 

 classed with the (juaternai-y, anrl that has been the constant 

 reference made; whether this treatment is a proper one must 

 be determined ))y additional work in the field. 



In general, the ridge may be said to be composed f)f ter- 

 tiar}^ strata of Eocene age representing the Claiborne l)eds of 

 Alabama. These beds contain many Claibornian fossils, 

 though the Ostreidce occur in the greatest abundance. The 

 localities in which these forms occur most numerously are 

 few and widely scattered, but are of the same age and of the 

 same value petrographically. The ridge is capped with de- 

 posits of loess that are the same in all essential features as are 

 the deposits in the regions farther north. These loess beds lie 

 directly upon the gravels of the Orange Sand, and are some- 



[Pkoc, L a. S.. .887-9.] 5a [Feb. 19, 1889.J 



