808 C. H. GORDON 
which Herrick! applied the term Manzano, from the Mountains of 
that name northeast of Socorro, in Valencia County, together with 
the limestones found overlying the sandstones in regions south of 
Bernalillo County, which Lee? has shown to belong to the series. 
Southward in Sierra County, where the Pennsylvanian and Lake 
Valley (Lower Carboniferous) formations occur together, the relations 
are those of apparent conformity. The Lower Carboniferous forma- 
tions thin out northward in Socorro County and are not known to 
occur north of the Ladrone Mountains. In the Magdalena Moun- 
tains the basal beds of the Pennsylvanian are conglomerates and 
shales, which rest with apparent conformity upon the Kelly (Lower 
Carboniferous) limestone. Northward in Bernalillo County the Penn- 
sylvanian rests unconformably upon granites and other rocks of 
supposed pre-Cambrian age. A well-marked unconformity occurs 
also at the base of the Manzano division east of Socorro, as shown by 
Herrick,3 who first recognized it and who states that this is evidently 
an unconformity by overlap. Lee+ has shown that the Manzano 
beds are separated from overlying formations by great erosional 
unconformity. The twofold division of the Pennsylvanian formations 
is sustained therefore both by faunal distinctions, according to Dr. 
George H. Girty,5 and by relations of unconformity as well. The 
faunal studies thus far made do not show any marked change in the 
life represented within each division, and the subdivisions are based 
entirely on lithological distinctions. 
THE MAGDALENA GROUP 
In general the Magdalena group may be said to be characterized 
by the predominance of limestone, while, on the other hand, sand- 
stones constitute the most prominent feature of the Manzano group. 
In Sierra County the Magdalena group consists for the most part of 
massively bedded blue and gray limestone, interstratified with which 
tC. L. Herrick, Journal of Geology, Vol. VIII, p. 115, 1900; Am. Geol., Vol. 
XXV, p. 337, 1900; Bull. Univ. New Mex., Vol. II, Fascicle No. 3, p. 4, 1900; Jour. 
Geol., Vol. XII, p. 244, 1904. 
2 W. T. Lee, zbid., Vol. XV, pp. 53, 54, 1907. 
3 Jour. Geol., Vol. XII, p. 244. 
4Ibid., Vol. XV, p. 54. 5 Ibid., p. 54. 
