The Classification of the Ordovician Rocks

Abstract

The classification of the British Ordovician Rocks has gone through many phases of instability in the past, and at the present time seems to be passing through another such phase. There are probably many causes contributing to this state of things, two of which seem to be fundamental; the first, the differentfacies of development exhibited in different districts by the formations making up the system; the second, the varied elements entering into the composition of the shallow water faunas apart from the considerations of facies; these would seem to be governed largely by possibilities of migration into the British region of the Lower Palaeozoic geosyncline from different directions, i.e. from America, from Northern Europe, and from Central Europe, so that a different type of “shelly” fauna characterizes the north-west and south-east margins.