strata with the Precambrian rocks. The Precambrian rocks consist of multiply deformed, metasedimentary, metavolcanic and metaplutonic rocks that range in age from 1.37 to 1.23 Ga. These metamorphic rocks have been intruded by 1.13 to 1.07 Ga, syntectonic to post-tectonic granites. These rocks can be divided into three fault-bounded blocks of strata called domains. They are called the Valley Spring, Packsaddle, and Coal Creek domains. Each of these domains contain distinctive rock types and ages and were either erupted, intruded, or deposited in three separate areas and later tectonically juxtaposed during the Grenville Orogeny. The Valley spring domain consists mainly of gneiss that is composed of quartz and microcline feldspar with minor biotite and hornblende. Likely, this gneiss consists of highly metamorphosed sedimentary, volcanic, and intrusive rocks that include rhyolite lava flows and ash-flow tuffs; igneous intrusions; and arkose interbedded with minor limestone, and shale. The age of these metamorphic rocks range from range from 1.29 to 1.23 Ga. The Packsaddle domain consists mainly of schists composed of hornblende, biotite, muscovite, and actinolite; marbles and calc-silicate rocks; quartzites; and quart-feldspar gneiss. These rocks were likely originally marine limestone, shale, and sandstone interbedded with mafic and felsic volcanic rocks and intrusive sills. They date from 1.27 to 1.25 Ga. Granitic sills that intrude these rocks have been dated from 1.255 to 1.250 Ga. The Coal Creek domain consists of a -long mass of serpentinite (The Coal Creek Serpentinite) that is surrounded by meta-igneous quartz-plagioclase gneiss of the Big Branch Gneiss. The gneiss has been dated at 1.33 to 1.30 Ga and was metamorphosed about 1.29 Ga, earlier than any other Llano metamorphic rocks. Coal Creek domain also contains diorite plutons, gabbro, amphibolite, mafic schist, minor talc, and smaller serpentinite bodies, all of which were metamorphosed about 1.26 Ga. The Coal Creek domain appears to represent fragments of an island arc with a slice of oceanic mantle faulted into it. After 1.2 Ga, a global cycle of continental collision and the resulting mountain formation, globally called the Grenville orogeny, and locally called the Llano Orogeny, tectonically shoved and interleaved together these strata. They were also further altered by metamorphism into the rocks that outcrop today in the Llano Uplift. Large granitic plutons that locally form a large percentage of the outcrop in some areas and a llanite dike also intruded them. During the 400-million year interval between the emplacement of llanite and