(also geol)
21rift valley — Geol. 1. graben. 2. a subsea chasm extending along the crest of a mid ocean ridge, locus of the magma upwellings that accompany seafloor spreading. [1890 95] * * * Elongated trough formed by the subsidence of a segment of the Earth s crust… …
22Ring of Fire — Geol. the linear zone of seismic and volcanic activity that coincides in general with the margins of the Pacific Plate. * * * Name given to a belt of seismic and volcanic activity roughly surrounding the Pacific Ocean. It includes the Andes… …
23ripple mark — Geol. 1. one of the wavy lines or ridges produced, esp. on sand, by the action of waves, wind, or the like. 2. one of such forms preserved in sandstone or siltstone. [1825 35] * * * One of a series of small marine, lake, or riverine features,… …
24shatter cone — Geol. a small, radially striated rock structure produced by intense shock, such as generated by meteorite impact. Also called pressure cone. [1945 50] * * * …
25sheet erosion — Geol. erosion by sheets of running water, rather than by streams. Also called sheet flood erosion /sheet flud /. [1915 20] * * * Detachment of soil particles by raindrop impact and their removal downslope by water flowing overland as a sheet… …
26S wave — Geol. a transverse earthquake wave that travels through the interior of the earth and is usually the second conspicuous wave to reach a seismograph. Also called secondary wave. Cf. L wave, P wave. * * * …
27tar sand — Geol. bituminous sand or sandstone from which asphalt can be obtained. [1895 1900] * * * or bituminous sand Deposit of loose sand or partially consolidated sandstone that is saturated with highly viscous bitumen. Oil recovered from tar sands,… …
28turbidity current — Geol. a turbid, dense current of sediments in suspension moving along the slope and bottom of a lake or ocean. Also called density current. * * * Underwater current of abrasive sediments. Such currents appear to be relatively short lived,… …
29Yule — (also Yuletide) noun archaic term for Christmas. Origin OE gēol(a); cf. ON jól, orig. applied to a heathen festival lasting twelve days …
30Cenozoic — (also Cainozoic, Caenozoic) adj. & n. Geol. adj. of or relating to the most recent era of geological time, marked by the evolution and development of mammals, birds, and flowers. Usage: Cf. Appendix II. n. this era (cf. MESOZOIC, PALAEOZOIC).… …
