The crystalline rocks of the Florida basement are predominantly ignimbrite, tuff, and agglomerate, generally of rhyolitic composition but including individual clasts and, in places, whole sections (e.g., Humble No. 1 Campbell and No. 1 Jameson) of intermediate or basic composition. Kaolinite in some ignimbrite may be a relic of Early Cretaceous weathering. Incomplete adjustment to greenschist-facies conditions is seen, especially in the less acidic rocks, but may be of local extent. Regional metamorphism is not recognized. Alteration to quartz and 1M white mica is present regionally but probably represents diagenetic alteration of primary glass in the presence of alkaline formation water rather than metamorphism in the strict sense.

Known intrusive rocks in Florida and Georgia are distributed sporadically except in an area of central Florida where a granitic province can be outlined. Granitic rocks are generally altered; specifically, in the Humble No. 1 Carroll the quartz monzonite is cataclastically shattered and veined but not pervasively sheared. The quartz-bearing hornblende diorite of the Sun No. 1 Powell Land Co. is a sill below which is hornfels derived from clayey volcanic-quartzose sandstone. The sandstone is the southernmost sedimentary rock known in the Florida basement.

The Amerada No. 2 Cowles Magazines Inc. penetrated diabase or trachydiabase overlying, and in apparent fault contact with, regional metamorphic rocks. These rocks are mainly quartz-bearing hornblende-andesine amphibolite containing layers of glassy-looking leucocratic quartz diorite gneiss that superficially resembles vein quartz. Retrograde metamorphism under conditions of the zeolite facies converted the amphibolite-facies rocks to quartz-albite-chlorite-prehnite schist along shear zones; in the surviving amphibolite and quartz diorite gneiss, it converted biotite to chlorite plus prehnite and produced dusty alteration products in andesine. During the waning stages of the retrograde metamorphism, tension cracks in amphibolite and quartz diorite gneiss were filled with laumontite, mo oclinic potassium feldspar, calcite, and chlorite(?).

The two southernmost basement wells penetrated basalt, perhaps presaging a distinct province of mafic extrusive rocks in southern or southwestern Florida, coincident with northwest-trending

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magnetic and gravity highs in peninsular Florida and a belt of irregular magnetic anomalies over part of the West Florida shelf. In the Humble No. 1 Keen the basalt is unmetamorphosed and unweathered. It resembles submarine basalt and may be related to buried seamounts, which are suggested by the magnetic anomalies over the West Florida shelf. The basalt may be much younger than the acidic volcanic rocks.

The age of the rhyolitic ignimbrite is unknown. Arguments can be presented for late Paleozoic, Triassic, or Jurassic ages, and also for a Precambrian age. The ignimbrite may belong to an extensive acidic igneous terrane that supplied considerable detritus to Cretaceous sedimentary rocks penetrated in the Cowles and Powell wells, and undoubtedly others.

The amphibolite of the Cowles well is 530 m.y. old, or older. It is probably in a branch of the Damaran (or Pan-African) orogen. The apparent event, about 530 m.y. ago, involved the amphibolite-facies and retrograde zeolite-facies metamorphism of the Cowles amphibolite, emplacement or metamorphism of the Carroll quartz monzonite, and, questionably, emplacement of the Powell diorite sill which is at least 480 m.y. old. Contact metamorphism by the sill may have affected already metamorphosed Precambrian rock or sediment derived at least in part from Precambrian source rock. The isotopic data on these points are conflicting. Meager data suggest that the diabase in the Cowles well may be of late Paleozoic, Triassic, or Jurassic age.