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). 



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