t» Hi Jin Aimrifdii ( rtii/iK/ist . DjToiiilitT, IWl 
tioiis for wiMtlu'iiiiu' action have \\vv\\ uioiv or less tavonihlc, 
especially as reuards the inteiveiitioii of moisture. 
-^ Iron- una i>f Kllxi. 
Tile specular iron-ores of the isliuul of Kll)a. which have often 
lueii instanced in text-books as an example of eruptive or huI>- 
limation (h'i)osits. a conclusion ([uestioned V)V (\. \o\\\ llath in the 
year 1S70. •*" liave since been described by Lotti of tlie Geological 
Survey of Italy, as in part altered products of replacement of cai- 
careojis rocks with which a cheniical interchange of materials has 
taken place, in conformity with the law that the more easily solu- 
ble minerals are replaced by the less soluble.! 
•A Ah/trlini iron- ores {7\ijjni). 
Among well-known Algerian iron-ores are those of thcTlemcen 
district, near the western border of the province of Oran. These 
ores, commercially known as Tafna ores, are, as descril)ed l)y M. 
Pouyanne. t hematites occupying the horizon of Liassic limestone, 
which rests unconformably on ancient crystalline schists. While 
masses, large and small, of unaltered limestone and siderite are 
nne(inally distributed in all of the workings, these masses all furn- 
ish evidence of gradual and progressive transition into hematite, 
while specular and magnetic oxides occur as products of further 
alteration. Other deposits imbedded with Tertiary stratti aie 
made up of detritus from the Liassic ores first mentioned. 
l^'^^•///■/M/^.//. I). C. Morrh 21, 1891. 
CRITERIA OF ENGLACIAL AND SUBGLACIAL 
DRIFT. 
B.v Wauukx Urii.v.M. SoiiR'i\ilU', >I:i>>. 
The purpose of this short paper is to call the attention of gla- 
cialists to the means of discrimination of the portion of the drift 
which, at the time of final melting of the ice-sheet, was enclosed 
within the ice and therefore is called englacial drift Ity I'res. 
Cliainbeilin. and the portion which was subglacial. lying undi'r 
the ice. It is hoped that the availability of the criteria here men- 
tioned will be discussed by others, and that we may attain the 
most useful methods of observation and di'terniination. in all parts 
of our drift-bearing area, concerning the question whether a large 
*.)ahrl). fiir Min. 1870, TSC. 
+ Kmnions, Trans. Am. Iii.st. Miti. Enu-. is><(». Fxt. H. 
:;:Aiin. iles .Mines i\, lS7(i, p. 81. 
