Page:VCH Northamptonshire 1.djvu/52

 A HISTORY OF NORTHAMPTONSHIRE have spoken of (p. i). Again; we notice that whilst the Nene and Welland rivers, and even the Ise, Harper and Willow brooks in the early parts of their course, flow in a north-easterly direction, the newer tributary streams of the Nene and the later-formed channels of the older ones take directions much more in accordance with the present dip of the strata, being even more southward than eastward (see map). All this points to a second uplift of the strata not in concord with the first, which, while it modified much of the drainage, could not divert the then well-established main lines of the rivers. The Northampton Heights The structure and formation of hills in general will be considered later, but this appears to be the proper place to speak of that range of heights bordering the county to the west and north-west, from north of Banbury to near Market Harborough, known as the Northampton Heights or Northampton Uplands. They form an almost uninterrupted fence to the county nearly approaching or exceeding 500 feet in height ; patches more than 600 feet above O.D. occur about Charwelton, Cold Ashby, Naseby and elsewhere, and some smaller spots reach to 700 feet or more, the highest point being Arbury Hill, 735 feet. These hills consti- tute a part of the diagonal water-parting of lower central England, and may be regarded as a continuation of the Cotteswolds. Now considering the height of the hills, the exceptional and very similar dip from all points of the compass ranging between south-west through west to north to- wards Northampton, confirmed by the direction of flow of the two main branches of the Nene to the same place (see map), we conclude that these hills represent the direction of that line of uplift which appeared to be called for by differences in direction of the earlier and later-formed valleys of the county. A diagonal elevation or fold, running approxi- mately from south-west to north-east, on crossing the area dipping to the Wash, would give rise to a curving of the Mesozoic outcrop towards the depression, just as we find it. No evidence is available to fix the time of the probable uplift we have been considering, but on the whole it is more likely to have occurred during the Miocene (or early Pliocene) than any other period, a time of great crust movements affecting a large portion of the earth, when both the Alps and Himalayas received their last great upward thrust, and when England acquired very closely the shape it now has, though it was not quite severed from the continent till later. The Pliocene Period Great earth movements, by affecting the distribution of land and water, would be likely to bring about changes in climate ; but whether we accept this as sufficient, or add to it astronomical causes, there is clear evidence that towards the close of the Tertiary — that is, in the Pliocene period — the climate was getting colder, and ultimately ice reigned supreme over Northamptonshire and all districts north of it. 22