Societies and Academies

Abstract

LONDON. Geological Society, April 18.—G. H. Mitchell: The succession and structure of the Borrowdale Volcanic Series in Troutbeek, Kentmere, and the Western Part of Long Sleddale (Westmorland). The area lies in the eastern part of the Lake District south of the High Street range. It is drained by the Rivers Sprint, Kent, and Trout Beck, all of which flow in a southward direction. Nine subdivisions are recognised in the rocks described. They have been subjected to severe earth movements. Two systems of folding are recognised, an earlier one of pre-Bala age and a later one of Devonian age. The former system, of simple character, shows axes trending in a north-northeasterly and south-south-westerly direction. In the latter the folding was intense, with an east-northeasterly and west-south-westerly strike, while the pitch of the folds was determined by the folds of pre-Bala date. The rocks are steeply folded in the south-east of the area, and the folds are even overturned to the north. Northwards the folding is less severe, and is marked by the presence of a broad anticlinal fold. No faulting of earlier date has been recognised. The rocks are strongly cleaved, the strike of the cleavage coinciding with that of the Devonian folding.—L. J. Chubb: The geology of the Marquesas Islands (Central Pacific). The Marquesas Islands, with one doubtful exception, are of volcanic origin. The southernmost, Fatu Hiva, consists of a caldera composed chiefly of lava-flows, within which an ashcone has been built up. The western half of the whole structure has disappeared, apparently owing to submergence by faulting. Motane is a small ash island. Tahuata is larger, and it also is composed chiefly of ashes in its northern part; its south-eastern side has been faulted down. In Hiva Oa there are three great craters in the western part, some of the coasts are faulted, and there is an elevated plateau at a height of 1300 to 1500 feet above sea-level. Nuka Hiva has a structure similar to that of Fatu Hiva, and it bears a plateau at an elevation of 2600 feet. It is considered that the group is situated, not on a crustal fold, but on a system of intersecting fissures. Elevation has occurred followed by subsidence. All the islands are surrounded by a shoreshelf, now standing, owing to a recent fall in sealevel, 3 or 4 feet above high-water mark. The poor development of coral-reefs in the group is due chiefly to periodic chilling of the water by extensions of the cold Peruvian Current, connected with cyclic climatic changes.