Art. V.] Herrick, Geology of New Mexico, 1 1 5 
with apparent conformability on a series of quartzites that form 
the transition into the metamorphic granites and gneiss below 
and the thickness of the quartzite often seems to depend on the 
amount of metamorphism to which it has been subjected. In 
some places the limestone seems to rest diretly on the granite 
but these cases may be interpreted as instances of extreme met- 
amorphism that have caused the qurtzite to assimilate to the 
granite. There seems to be every reason to suppose that the 
band of quartzite is of a different age from the granite as well 
as to believe that the granite itself is of sedimentary origin. 
The basal quartzite is usually from fifty to seventy-five feet thick 
while it may drop to ten or twenty feet. A few fossils have 
been found in the upper shaly layers but they probably belong 
rather to the shales which next follow. These shales are fre- 
quently highly metamorphic but are fossiliferous. The quart- 
zite has conglomeritic phases with granitic and other pebbles. 
It reminds one by position and lithological character of the 
basal conglomerate lying under the coal measures of Ohio and 
Pennsylvania but no homology is suggested. The conglomerate 
quartzite is frequently the catch-basin for the leechings of the 
limestone and sand-stone above and accordingly is of some im- 
portance as a collector of intrusive ore. See account of the 
Caballo mountain ore in another place. 
Immediately above the quartzite is usually a band of shale 
of about ten feet followed by perhaps 150 feet of fossiliferous 
limestone. It is in the shaly beds in this horizon that the most 
abundant fossils are to be found. Spirifer opima, Productus 
cora, Martinia concentrica, etc., are the characteristic species. 
In typical sections this lime is followed by about twenty- 
five feet of conglomerate or sand-stone. There follows about 
three hundred feet of limestone which tends to grow lighter to- 
ward the top. This is not very abundantly supplied with fos- 
sils. It may be separated from the next member by a thin 
band of bandy shale. In many exposures the next fifty feet is 
the prominent portion of the series it being a specially massive 
and permanent band of limestone. The next 125 feet is frag- 
ile and contain Productus nebrascensis (?) and large Spirifers 
