G. H. Williams—Norites of the “ Cortlandt Series.” 197 
like the fibrolite, is exceptional, but by no means unprece- 
dented, as may be seen from the above description of the Rons- 
sperg hercynite. In the Cortlandt deposits the distribution of 
the corundum is so irregular as to’seriously interfere with its 
practical value. Specimens in which it is comparatively abund- 
ant are not to be distinguished, except under the microscope, 
from those which are entirely free from it. How far this is 
true may be judged from the fact that the purest specimens of 
pleonaste which the writer obtained anywhere in Cortlandt 
township were taken from the pile of “emery ore” in the yard 
of the Peekskill emery mill. This so reduces the grade of the 
Cortland product as to practically rule it out of the market. 
The following seven analyses of the Cortlandt ore were made 
in 1880, for, the New York Emery O©o., of Peekskill, by Prof. 
Th. Egleston of the Columbia College School of Mines. They 
are here published for the first time with the permission of 
their author. 
i IDL, TTT a elas Vis WALES A) Nall 
INAQ)s Six alee See een eae 31:93) 40°77) 37°78} 37°43) 36°49) 41°66} 46°53 
Hes One eye a eee SN SNO ule: Siilgades 5ilre alenue leds Gllluea SOM lia sae siE 
WD Be Bees a ee ae eA sii neg 2 e210 W823 Olio) 9°43 
Maeoneticsiromys22. 226 es 34°20) 32:01) 17-37%) 19°81) 22°77) 14:76) 8:98 
Siliceous residue _--_._---- 6°42; 1:04) 11:19} 13:14) 10°08) 11°48) 2°42 
Ek @) ye Mena BO wireaivl Sites) Soi LAGOS ORG: OSGo ea OLN) MOs4 aa Ozbil 
SUT po ray eee eae he eee ae 0:04) 0-04) 0°02) 0°02} 0:02} 0:01) 0-01 
EOS pHOnuU Seems ae eens trace | trace | trace | trace | trace | trace | trace 
eR Otenl eaepaenes Pes sa g2h, Nek 99°31, 100-04] 99-25) 99-42} 99-78] 100-07| 100-19 
| 
If from these analyses all the components except the alum- 
ina, magnesia and iron be deducted, and if these be calculated 
in proportions of 100 after the ferric iron has been reduced to 
its equivalent per cent of ferrous iron, we shall have: 
| | | | 
Tee) Te TA) Save aver lov teals Nolte iMfean 
a ee Pee | | 
Oe at 2 | 53°63) 60.00] 51-94| 54-92) 53-18| 54-88) 50°65] 54-17 
Ose Le | 33°92| 30°05] 37-18| 34:52| 34:59) 34°70) 39-08] 34-84 
Ome | 12-45| 9-95] 10°88} 10°56 12-23| 10-42) 10-28] 10-96 
Sie ee | | 
Maralyn S28). 2) 100-00, 10000) 100-00) 100-00, 100-00, 100-00 100-00] 100-00 
| 1 
A glance at these analyses is sufficient to show that a very 
large proportion, if not all, of the samples consisted of pleo- 
naste. Still, the microscope discloses the presence of true 
corundum in many specimens, although its amount is very 
variable. ‘ 
