•220 Beeby Thompson — Use of a Geological Datum. 



Salt water came from the bottom of the boring and rose to within 

 8 feet of the surface. 



This boring is situated about two miles from the Kettering Road 

 boring, and in a nearly direct line between the latter and Gayton 

 boring. It is on the south side of the Nene ' fault,' and not far 

 removed from it ; also, notwithstanding that the Marlstone rock-bed 

 is not present, or at least was not recognized, I am convinced that 

 the Middle Lias is nearly complete, the upper part being represented 

 by what is described above as "dark tenacious clays with erratic 

 boulders " to the extent of about 20 feet out of the 46 feet. This 

 belief is founded on personal inspection of material brought up 

 from a well on the same side of the Nene ' fault,' starting at 

 approximately the same level above O.D. and only about a quarter 

 of a mile away to the north, at Messrs. Phipps' Brewery, and from 

 the fact that at two places a little nearer the line of the river Nene 

 alluvium and gravel combined had the thickness of 27 feet and 

 28 feet respectively. 



Keferring again to the same section, when it became evident that 

 the combined thickness of Middle and Lower Lias was nearly 

 identical with the thickness of the same formations at Gayton 

 (see Summary of Borings), then also it became highly probable 

 that the very hard pyritons rock, 1 foot thick, immediately under 

 the Lower Lias was the equivalent of the hard white limestone with 

 pyrites, 1 foot thick, similarly situated at Gayton/ both, in fact, 

 constituting the top of the White Lias. 



Levelling each of these rocks to a Marlstone datum of + 107 feet 

 O.D., as in previous instances, we get the Gayton hard limestone 

 coming out as — 466 O.D., and the Northampton, Bridge Street, 

 hard pyritous rock as — 463, or a few feet below this if we make 

 allowance for the slight imperfection of the Middle Lias there. 

 Anyway it is obvious that these rocks were deposited at practically 

 the same depth at the same time. Thus the Ehsetic beds are 

 virtually brought into Northampton, and the suggested cause of 

 their absence in normal form two miles away, at the Kettering Road 

 boring, is made a certainty. 



Orton. — After correcting for the post-Liassic earth -movements 

 (p. 218), and placing on to the Old Land Surface at Gayton 

 118 feet, and at Orton 49 feet (aggregate of Trias, Littoral Beds, 

 and Ehastics), then the top of the Rh^tic beds at Orton would 

 be 45 feet lower than at Gayton ; and it might be asked why, in 

 accordance with the gist of this paper, the whole of the Rhaetics 

 are not present at Orton, or inversely why any whatever are present 

 at Gayton. I cannot here deal with the whole subject involved 

 in an answer to such a question, but chiefly and briefly my reply 

 is this: — Orton, at the close of the land period, was higher than 

 Gayton (smaller thickness of Trias and Littoral Beds) ; at the 

 latter end of the Rhaetic period at about the same level (indis- 

 tinguishable nature of some of the deposits from the two places) ; 



1 Henry John Eunson, F.G.S., "The Range of the Palteozoic Eocks beneath 

 Northampton": Quart. Joui-n. Geol. Soc, vol. xl, pt. 3, No. 159, p. 486. 



