/ 
C. H. Hitcheock—Helderberg Rocks in New Hampshire. 45 
lies the supposed Coés quartzite, with a strike differing from 
that of the latter as much as thirty or forty degrees. I do not 
find any regular gneiss in the Cots group anywhere in the 
State. It is a curious fact also that there are extensive ranges 
of what seems to be the Cods quartzite resting unconformably 
upon the gneiss, without any connection with mica or horn- 
blende schist, They must continue to be ranked as Cdos till 
we have evidence to the contrary. The Cods group may also 
embrace the ‘“calciferous mica schist” of Vermont. The orig- 
inal definition of this group expressly excluded the latter rock. 
Further study will be required to make this position a sure one. 
Errors have arisen in consequence of confounding the Cods 
group with the White Mountain series. Dr. T. Sterry Hunt 
has included these two series in one, which is stated to be 
pre-Cambrian, with the name of Montalban. Originally he 
grouped them under the provisional name of Zerranovan, and 
presented considerations leading to the belief that they might lie 
near the horizon of the Potsdam. As already shown elsewhere, 
it is better to separate the Cods and White Mountain series, 
though both abound in the related silicates, staurolite and an- 
dalusite. The latter may be pre-Cambrian, but the former can- 
not well be older than Cambrian; and Professor Dana thinks 
the Bernardston region proves all the Cods rocks to be of Hel- 
derberg age. : 
N consequence of Dr. Hunt’s error just cited, Prof. Dana has 
also misapprehended the relations of these two systems, sup- 
posing that Dr. Hunt had used the term ‘“ White Mountain 
series” in the same sense in which I had previously employed 
it, In my 1869 report. He says:* “A large part of the rocks 
that have been distinguished as of the “ Montalban” or White 
Mountain series in New Hampshire, and regarded of pre-Silurian 
age, are here included, and are hence nothing but altered Hel- 
derberg sediments.” He then quotes from Dr. Hunt's Indian- 
apolis address the names of the rocks belonging to this series, 
which include both the Coés and White Mountain series. If it 
certainly enter the area represented upon the map, and hence 
any notice of it here requires an apology. It is mentioned only 
cause it has been erroneously associated with the Coos group. 
e two series are unlike in mineral character, thickness and 
Seographical distribution. : 
8. Swift Water Series.—This will be defined in the next issue 
of the Journal, 
* This Journal, ITT, vol. vi, p. 348. 
