Terebratula. A fossil shell.
Tertiary strata. The series of sedimentary rocks overlying the chalk, or other representative of the Secondary period, and extending thence to the rocks of the Recent period.
Testacea. Molluscous or soft animals having a shelly covering.
Thecodont. A fossil saurian or marine lizard.
Thermal. Hot. Thermal Springs are springs whose temperature is above the mean annual temperature of the place where they break out.
Tetrapterous. Four-winged.
Tibia. The principal bone of the leg.
Toad-stone. The name given by miners to beds of basalt, occurring in Derbyshire.
Trachyte. A feldspathic variety of lava.
Trap. Crystalline rocks, composed chiefly of feldspar, augite and hornblende, combined in many ways, and exhibiting great varieties of aspect, are frequently called by this name.