Archean felsic volcanic rocks in felsic rocks. Timing of felsic volcanism and tectonic constraints can be identified by radiometric dating and isotopic analysis. In Archean, underwater eruptions of felsic lava were common. Submarine eruption is evident by coarse volcanic breccia formed in situ, hyaloclastite or underwater pyroclastic deposits (clastic rock, composed of tephra only). Since felsic magma is viscous, volcanic eruptions that form dacite or rhyolite are explosive and violent. The Archean felsic eruption may be assigned to Vesuvius eruption type in the present day. Submarine rhyolitic flows were widespread in Archean but it is uncommon in the modern volcanic environment. Viscous felsic eruption
Grayson Glades Natural Area Preserve Grayson Glades Natural Area Preserve Grayson Glades Natural Area Preserve is a Natural Area Preserve located in Grayson County, Virginia. Its centerpiece is an extremely rare wetland type known as a "mafic fen", which are situated upon soils rich in magnesium and fed by springs. The site is at the headwaters of a small stream system supporting additional mafic fens. Among the rare species found on the property are tuberous grass-pink ("Calopogon tuberosus"), ten-angled pipewort ("Eriocaulon decangulare" var. "decangulare"), large-leaved grass-of-parnassus ("Parnassia grandifolia"), queen-of-the-prairie ("Filipendula rubra"), sticky false-asphodel ("Triantha glutinosa") and Canada burnet ("Sanguisorba canadensis"). The preserve is owned and