LEIDSE GEOLOGISCHE MEDEDELINGEN, deel 41, pp. 153—220, published separately 15-11-1967 The geology of the Upper Ribagorzana and Baliera valleys,Central Pyrenees, Spain BY

In the mapped area there is a well-exposed low-grade metamorphic marine sequence from Ordovician to Lower Carboniferous, unconformably overlain by Permo-Triassic continental deposits. Determinable fossils are rare. The Ordovician consists of a quartzite/shale sequence with one marly limestone intercalation in the upper part. The Silurian is developed as a classical graptolite-bearing black shale facies with an Orthoceras limestone near the top. The Devonian rock-sequence in the north differs from that in the south. The northern or Sierra Negra facies area consists of a thin (120—250 m) alternation of mainly limestone and slate; the southern, Baliera facies area, is thicker (340—780 m), shows more individual limestone-slate units, and is moreover characterized by a conspicuous quartzite member (0—50 m) in the middle part of the Devonian. The Devonian sequence in both areas is subdivided into four or five separate formations which have been mapped individually. The Carbo-niferous consists in both areas of micaceous slates with a low sand content. The continental Permo-Triassic is developed in the Germanic facies of red mud- and silstones, sandstones, and conglomerates at the base, followed by a non-fossiliferous limestone/dolomite (Muschelkalk) and gypsum-bearing, vividly coloured marls of the Keuper. The major structural movements, which probably began already in early Carboniferous times, increased in strength towards the Westphalian B. Several phases of deformation have been recognized. The first deformation produced concentric, open to tight asymmetric folds without cleavage development. Their axial planes have a general E-W to ESE-WNW tren