8Io CH. GORDON 
assumed conditions of deep and clear waters wherein were deposited 
the extensive limestone beds which constitute the upper part of the 
division (the Madera limestone). 
Northward in Socorro, Valencia, and Bernalillo Counties the 
Magdalena division comprises from 1,000 to 1,300 feet of sediments, 
the character of which in their typical locality will be seen from the 
section on p. 807. a 
The rocks of this division contain a characteristic Pennsylvanian 
fauna, which shows no essential variation from the base to the top of 
the series, but on lithological grounds they are readily separable into 
two formations, to the lower of which Herrick! gave the name Sandia 
Beds (or series), from the Sandia Mountains, where they were first 
studied, while the upper is known as the Madera limestone.? 
Sandia beds.—In Socorro County the Sandia formation consists of 
alternating beds of blue and black clay shale, compact earthy lime- 
stone, and conglomerate, vitreous sandstone or quartzite, the shale 
and limestone predominating. In places, the shales are highly car- 
bonaceous and sometimes show traces of coal, but thus far no coal 
beds of importance have been discovered in this formation. The 
sandstones are usually hard, with a vitreous fracture, and present the 
characteristic appearance of quartzites. The beds are often con- 
glomeratic, the included pebbles consisting for the most part of pure- 
white quartz. The basal beds of the series in the Magdalenas, 
comprising a thickness of ten to fifteen feet, consist of a moderately 
coarse conglomerate interbedded with dark shale. While these 
beds rest apparently conformably upon the limestones below, the 
relations are undoubtedly those of unconformity. About 125 feet 
above the base of the series is a formation of coarse white quartzite 
or conglomerate in massive ledges separated by thin beds of shale. 
Some of the quartzite beds are filled with pebbles. Overlying this 
is a limestone formation eighty to ninety feet thick, in which appear 
some thin beds of shale and quartzite. At the base of this imestone 
formation is a thick-bedded dark-blue subcrystalline limestone six 
tC. L. Herrick, Jour. Geol., Vol. VIII, p. 115, 1900; Am. Geol., Vol. XXV, p. 
235, 1900; Am. Geol., Vol. XXXIII, p. 310, 1904. 
2C. R. Keyes, ‘“Water-Supply Paper No. 123,” U.S. Geological Survey Report, 
1904. 
