It is interesting to notice, as an illustration of the now well established fact that successive earth movements often occur in the same direction, that the axes of the folds produced during this second continental (Devonian) period, run parallel with the lines separating tracts of different lithological characters. It has been seen that the Ordovician and Silurian rocks of the Southern Uplands continue into Ireland, and that the beds of similar characters run in belts having a general east-north-east and west-south-west trend, which accordingly must have been the direction of the coast-line parallel to which they were deposited, and as that coast-line was due to uplift, the movement which produced it would naturally produce foldings with east-north-east and west-south-west trend. This is one of many cases where the lines separating belts of rock having different lithological characters run parallel to axial lines of folds which have been produced in the rocks at a later period. As the result of the existence of land over parts of north-west Europe in Devonian times, it is comparatively rare to find a passage from normal Silurian rocks into normal Devonian ones; there is often an unconformity above the Silurian strata. As we proceed southwards towards central Europe, where the epeirogenic and orogenic movements died out, this is not the case, and we get complete conformity between marine sediments of the Silurian and Devonian periods. CHAPTER XVII. THE DEVONIAN SYSTEM. _Classification._ As a result of the movements which were briefly described in the last chapter, two types of Devonian deposit are found in the British Isles, and are called respectively the Devon type and the Old Red Sandstone type. The latter rocks, formerly divided into three divisions, are now separated into two only, the upper and lower Old Red Sandstone, and the exact relation of these to the different subdivisions of the rocks of Devon type remains to be settled. The Devon type itself has given rise to much difference of opinion, two local classifications have been applied, one for the rocks of North Devon and another for those of South Devon. The classification which has been most generally adopted is as follows:-- N. Devon. S. Devon[83]. { Pilton Beds { Entomis Slates Upper Devonian { Cucullæa (Marwood) { Goniatite Limestones (Clymenian) { Beds { and Slates { Pickwell Down Sandstone { Massive Limestones Middle Devonian { Morte Slates { Middle Devonian (Eifelian) { Ilfracombe Beds { Limestones { Ashprington Volcanic { Series { Eifelian Slates and { Shaly Limestones