GEOLOGY p. 2) — representing a period of time during which deposits of the aggre- gate thickness of some 20,000 feet were formed in other localities — and it be asked what was happening here, the answer is clearly this, that the denudation which did not finish till late in Triassic times com- menced a great deal later than the Lower Carboniferous period, or there could otherwise have been none of the Carboniferous Limestone left. In other words, there must have been a very considerable thickness of rocks for denuding agents to act upon, over the Carboniferous Limestone now found, and these may well have included the Coal Measures. The Permian and Trias. The Mountainous Period A termination to the long Carboniferous period appears to have been brought about by extensive earth movements in the part of the world embracing what is now England, by which great arches (anticlinal axes) and corresponding troughs (synclinal axes) were formed, having directions approximating more nearly to east and west than to the other cardinal points. In the troughs the Permian rocks were deposited, and any Coal Measures below preserved for the time being, whilst the ridges were exposed to denudation, and the coal originally on them swept away. At the close of the Permian period a new series of earth movements resulted in the formation of other ridges along approximately north and south lines.* It was this later series which completed the Pennine chain, the great central ridge of the north of England. The two sets of inter- secting ridges divided the coal formations into groups of depressions, commonly called basins, and in the partially land-locked hollows so produced the Trias beds were deposited, whilst the newly-formed ridges were being denuded of both Permian and Coal Measures. Northamptonshire shared in one or both of these earth movements, and throughout the greater part of the Trias, if not also the Permian period, was largely a land surface, subject to denudation, and during the later stages at least, as the Carboniferous Limestone and other older rocks got exposed, acquired an appearance comparable to that of the moun- tainous parts of Derbyshire now. Still, it may be pointed out, the problem of finding coal in Northamptonshire remains unsolved. The conclusion of the Paleozoic period in geological history, and the slightly later closing of the long land period over Northamptonshire, left then a very uneven surface, mostly of limestone, as a foundation upon which the main mass of the well known stratified rocks of the county were afterwards piled almost uninterruptedly through some millions of years. THE BUILDING UP OF NORTHAMPTONSHIRE To appreciate properly the character and proportions of the Jurassic architecture of Northamptonshire, it is necessary to take a glance at conditions over a larger area. We have spoken of earth movements resulting in folds of the rocks ; these were merely wrinkles in a vast ' Edw. Hull, Tht Coal Fields of Great Britain. 7
