The Pennsylvanian Period was a time of coal making on the greatest scale in the earth’s history. Extensive swamps and marshes, the habitat of peat and ultimately coal, were almost lacking in New Mexico. Thus, only thin scattered lenses of coal occur in the Pennsylvanian beds of the state. The lands of this period were covered by tree ferns, scale trees, horsetail rushes, and primitive conifers. In the shallow seas, the dominant invertebrates were fusulinids (fig. 8), small-shelled protozoans shaped like grains of wheat. Abundant cockroaches, large dragonflies, and spiders swarmed over the land. [Illustration: Figure 7. New Mexico during Pennsylvanian time] Permian Rocks The Permian Period (230 to 280 m.y. ago) dawned with renewed rising of the highlands in northern New Mexico and southern Colorado. Floods of red sand and clay, washed from the rotting hills, wiped out the seas of northern and central New Mexico, and intertongued southward with marine limestones. These early Permian rocks are the Hueco Limestone near El Paso, there 2200 feet thick, the Abo Redbeds near Albuquerque, and the upper Sangre de Cristo Redbeds southeast of Santa Fe. Wherever the redbeds crop out, their dark reddish brown hue, speckled and striped with spots and streaks of green, enlivens the drab gray-and-brown landscape. Some of the reddish coloring is from angular grains of red to orange feldspar, but most is in thin brilliantly tinted skins of hematite that coat the sand grains and saturate the clays. In northern and central New Mexico, amphibians and other primitive vertebrate animals lived amid the red soils and sands; their bones and imprints have been preserved on thin flat slabs of sandstone that now decorate sidewalks and patios. Figure 8. Fossil specimens [Illustration: Bryozoan _Fenestrellina._] [Illustration: Fusulinid _Fusulina._] [Illustration: Coral _Lophophyllidium._] The early Permian seashore, where limy muds beyond the surf intermingled with red sandy muds swept from the north, vacillated somewhere north of Alamogordo with each sea-level change. Amid the breakers, and as submarine banks in the shallow waters, reefs grew—moundlike masses of shell debris and calcite mud trapped among frondlike calcareous algae. Near Tularosa, these algal “bioherms” are sixty feet high and extend within broad belts half a mile wide. In southeastern New Mexico, these buried “Abo” reefs have yielded much oil.