RN \-:k\ns\s. 



tn h' iTcouiii /.(■(! williiii l!iis area must h" liascd ii|)(iii >trati- 

 irraphic niul pctrouraphi ■ ralln'r lli.iii upon pala'oiitoloLjir 

 <iat:i. 'riic paucity of fossil i-('iM:iiii< in all fns>ilifcrous (li\i>- 

 ions, cxccpl ill thai whicli is tcut.itivcly, luTciii, dciioiiiinatcd 

 till' Ostrca l)c(l. and the ahsolulc doart Ii of such ivinaius in 

 most of the strata lit iKtlo^ically rcco^ni/cd as Koccnc tertiary 

 precludes a classiti'-alion based upon thoii-fauiial contents. As 

 has been above indicated the fa( ies of the fauna which has 

 been collect'd and studied ajtMears to necessitate tjje corj-ehi- 

 tiou of the lowest l)eds with the ClaiboiMiian . 



To sum up the strati^raphic oi' ireoloijic jiistory t>f ("I'ow- 

 ley's Ridue and with it that of the reirion of which it f(»rnis u 

 <'()nsiderable topoii'i'iiphic feature it may be said that tlie rid,ir<* 

 is the remains of a former extensive jjlateau, the western limit 

 of which was the i)aliVo/oic scarj) of middle Arkansas, as 

 noted above. That erosion occurred fi-om the M'ost, l)y the; 

 waters which ai'e now i-epreseuted by the \\'hite Kivei- and 

 other streams, to which, nearly at the northern boundary of 

 the State, the Mississippi ad(h'd enormous vohimes of water, 

 either continuously or periodically. These did their work so 

 completely that the whole of the country between Crowle}'':^ 

 Ridsre and the paheo/oic rocks on the west has been lowered 

 and carried away except where a few^ unimportant secondary 

 ridijes, such as that at Auo'usta, in Woodruff County, remain 

 to bear witness to the past former height of the whole coun- 

 try, 'i'o the. eastward the Mississi})pi was enira<ifed likewise 

 in the work of destruotion and denudation, plouLrliinij- out an 

 immense trough to which the pres(>nt Mississippi bed is but 

 the merest pigmy, lint while it dug its valley wider it also 

 dug it deeper. \or has the retilling which foi' ciuituries has 

 been occurring yet brought the eastern level u[) to that west 

 of Crowley's Ridire. Dui-ing tli" jirogress of denudation, t!ie 

 whole southern basin of the Mississijipi was slowly sinking, 

 til" tiulf traveled northwards, until ('r(»wlev"s Hidire became 



