224 The Aincn'cdit Geolcxjisf. April, 1895 
MIOCENE: THE (JKANU (iUEF GUOUr. 
'J'lic Miocene of Louisiana is represented by tlie (Jraiul (iulf 
group of Ililgard. These rocks have l)eeii described l)y Hil- 
gard, Hopkins, Johnson, and Lerch. 
They are composed of claj^s, sands, chtystones, sandstones, 
and quartzites. So far no fossils have been collected and de- 
termined from them, but they are referred to the Lower Mio- 
■cene because they are without doubt the same as the Grand 
(Julf of Mississippi, the age ofwhich has been fixed positively.* 
The northern boundary of the (Jrand Gulf has already in 
part been indicated in this paper. It runs north from Harri- 
sonburg, flanking the bottom of Ouachita river, to a point 
about three miles south of Rosefield. The line from this point 
to the Red river has alreadj^been indicated. West of theKed 
river there are excellent exposures at ( 'hopin. Thence the line 
has been traced to the Sabine river by Hopkins. After cross- 
ing the Red river Hopkins says : "Rejippearing in the Cloutier- 
ville and Kisatchie Hills, it ranges ahnost due west to the 
'Bad Hiir seven miles south of Man}', in De Soto, and reaches 
Sabine, near the mouth of Bayou Negrut."f 
The relation of the Grand (^ulf to the Eocene is a perplex- 
ing question, and is one not satisfactorily settled, Pumpelly;|; 
and Dall§ have shown that in Florida the lowest Miocene rests 
unconformably on the Vicksburg Eocene. We have in Louis- 
iana the Vicksburg Eocene and the Lower Miocene. 
The topographic features of the Grand Gulf are interesting. 
The northern boundary is, when not covered by the subse- 
(juent deposits, a rather steep escarpment facing inland, un- 
derneath which the Vicksburg ilips. Dr. Lerch has given an 
excellent description of the topographic features of the Grand 
Gulf. 
Mori' tliaii any u\ \Uf prcNious I'cuidiis (icscribt'd, il lias the plain 
siructui-c preserved, tlioiigii erosion luis been in tliis territory not less 
actiseil lias cliiseied out dilferenl forms. Instead of tlie well rounded 
hills and more jjentle slopes of the ridues occupyinji: llie region north of 
ils boundary, il slopes from its deeply dentated and broken nortii line 
*l)all. Hull, tieol. Soc. .Vmer.. vol. v, 1894. pp. 1(54, 1(57. 
Smith. Am. .lour. Sci., Ill, vol. XLvii, p. "ilX), Ai)ril. 1804. 
Smith. Charl to Geol. Map of Ala., 18!)4. 
[Hopkins; First Ann. Rep., (Jeol. Surv. La. for 18(5!), pub. 1870, p. !»!». 
|.\mer. .lour. Sei.. III. vol. xi.vi. p. 44.') el seep, 18!):{. 
iliullelin (;eol. Soe. .\m.. vol. v. p. Hi-.'. 18!M. 
