A HISTORY OF NORTHAMPTONSHIRE at either Gayton or Orton, as it should be according to this contention ; also, as Mr. Eunson observes,' the lower part of the Lias clay at North- ampton has a more sandy appearance and uneven bedding than was observed at the other two places, indicating nearness of the material from which it was formed and shallow water dispersal of the same. The Lower Lias For a long time following the Rhjetic period, as far as we can judge, the general tranquil sinking continued over a very large area. At first the sea was shallow, and we find evidences of proximity to land in the remains of insects in the lowest beds of the Lias. We may consider that some Carboniferous Limestone was left exposed for a long time in the direc- tion of Rugby, which, by its disintegration into calcareous mud, and admixture with argillaceous matter from a more distant source, formed the succession of marls, also assisted by dissolved carbonate of lime in a warm shallow sea the numerous alternating beds of argillaceous limestone so characteristic of the Lower Lias limestone quarries around Rugby. Higher in the formation, and therefore later in time, the Lower Lias is a more purely argillaceous deposit, and although stone beds do occur at intervals, they are often composed of fossils. Irregularly disposed argillaceous nodules, or cement stones, occur throughout the formation, but the exact origin of these has not yet been demonstrated. The Lower Lias as a surface formation skirts the western and north- western parts of the county from near Banbury to near Market Har- borough (see map). It is exposed along valleys converging to Weedon, but not so much as the map indicates. The average thickness, deduced from the various borings, may be put at 520 feet ; this is less than is usually quoted because the thickness of the Middle Lias has, until lately, been much underestimated.^ It may be that every well-recognized Palaeontological zone of the Lower Lias occurs in Northamptonshire, for they have all been found within or near the borders ; they include xhtzontsoi Ammonites planorbis, A. angulatus, A. bucklandi, A. semicostatus, A. tumeric A. obtusus, A. oxynotus, A. raricostatus, A. armatus, A. jamesoni (with sub-zone A. pettos), A. ibex, A. henleyi, A. capricornus^ We have not thought it necessary to give a very detailed account of the Lower Lias because there are few exposures in the county. The following particulars will give an idea as to where it may be studied. The Ibex, Henleyi, and Capricornus zones were passed through in making Kilsby tunnel ; the Ibex zone can be seen at Welford and Braunston ; the Henleyi zone at Buckby Wharf; the Capricornus zone at Little Bowden,
- Henry John Eunson, * The Range of the Palxozoic Rocks beneath Northampton,'
Quart. Journ. Geol. Soc. (Aug. 1884), vol. xl. p. 492.
- Beeby Thompson, ' Excursion to the New Railway at Catesby, Northamptonshire,'
Proc. Geol. Assoc, vol. xiv. pt. 10 (Nov. 1896), pp. 65-88. ' Beeby Thompson, 'Excursion to the New Railway at Catesby, Northamptonshire,' Proc. Geol. Assoc, vol. xiv. pt. lo (Nov. 1896), pp. 65-88 ; 'Geology of the Great Central Railway, Rugby to Catesby,' Quart. Journ. Geol. Soc, vol. iv. (Feb. 1899). 10
