The great copper-mining district of Southern Spain and Portugal has been studied by several eminent geologists, and the problems presented in the geology of the field and of its ore-deposits have given rise to conflicting opinions. The three most debated points have been the origin of the ore-deposits, the relations of the igneous rocks, and the age of the sedimentary formations. The present paper, the field work for which was carried out during the last summer season, deals in the main with the two latter points, and the writer takes this opportunity of expressing his indebtedness to Professor W. W. Watts and to Dr. C. G. Cullis for their advice and suggestions during the subsequent petrological studies at the Imperial College of Science and Technology, London.