Societies and Academies

Abstract

Geological Society. Frbruary 5.—Sir Archibald Geikie, K.O.B., Sec.R.S., president, in the chair.—Antigorite and the Val Antigorio, with notes on other serpentines containing that mineral: Prof. T. G. Bonney. It is not certain that the first described specimen of antigorite was really found in the Val Antigorio. The rock probably does not occur there in situ, though it is found in pebbles, &c., from tributaries. Other specimens of antigorite-serpentine were described. The origin of the mineral is discussed. Pressure is essential; it can be formed from augite, and there is evidence of its coming from this mineral.—The St. David's Head “rock series” (Pembrokeshire): J. V. Elsden. These intrusions are of complex composition. There is a high magnesia percentage. There is no evidence of differentiation in situ, but the facts suggest a common origin from a differentiated magma basin. The rocks afford facilities for the study of both rhombic and monoclinic pyroxenes. Rhombic pyroxene generally crystallised earlier than the monoclinic pyroxene. There are two varieties of augite. The relation of these types lends support to the perthitic theory. The probable age of the intrusions is not greater than that of the earth movements which folded the Arenig shales in this district.