Beehy TJiompson — Use of a Geologicril Datum. 



219' 



Table showing Variations or Level due to Earth-Movements. 



Height from Ordnance Datum in feet. 



Present actual levels : top of Middle Lias 



,, ,, Old Land Surface 



Restored relative levels : top of Middle Lias 

 ,, „ Old Laud Surface 



Significant records 



Gayton. 



+ 274 



-417 

 + 107 



\ 



\ 



-584 



Rhsetic Beds, 



36 feet. 



Northampton. 



+ 107 



-527* 

 + 107" 

 -527* 



Orton. 



\ 



No 

 Ehsetic Beds. 



^326 



-341 



+ 107 



-560 



Ehsetic Beds,. 

 22 feet. 



Gayton. — After having made our correction for earth-movements 

 subsequent to the Middle Lias period, if we pile the 82 feet of Trias 

 and Littoral Beds on to the Old Land Surface at Gayton, and the 

 67|- feet of similar beds on to it at Northampton, it will still leave 

 Northampton 42 feet the higher, an amount of difference in level 

 suflScient to entirely exclude the 36 feet of noi'mal Ehsetics found 

 at Gayton only about five miles away, in strict accordance with 

 our specification of a datum rock, though very probably the upper 

 portion of the Littoral Beds at the Kettering Road are of Rhsetic age. 

 The addition of 36 feet of Rhjetic beds at Gayton would, however, 

 bring the levels of the two localities, Gayton and Northampton, 

 within 6 feet, consequently this is the amount of diffei'ence in 

 aggregate thickness of the Middle and Lower Lias at the two places 

 (see Table). A very small amount, it will be observed, out of 

 570 feet, considering that the places are about 5 miles apart. 



Northampton (Kettering Boacl), — It follows from the above con- 

 siderations that the Littoral Beds at the Kettering Road boring, 

 Northampton, may be of an age extending from the Triassic, through 

 the Rhgetic, even into the Lower Liassic periods. This will help 

 to explain the abnormal character of the deposits themselves, and 

 also the sandy nature of the lower beds of the Lower Lias there, 

 for, no doubt, land remained exposed and the sea shallow to a still 

 later period than at Northampton, not far away. 



Northampton (London and North- Western Bailway, Bridge Street 

 Station). — The account of this boring left by the Rev. C. H. Harts- 

 horne ^ runs as follows : — feet. 



Superficial accumulation, consisting of detrital gravels, dark 

 tenacious clays with erratic boulders ... ... ... ... 46 



Lias blue clay with bands of stone ... ... ... ... 550 



Very hard pyritous rock ... ... ... ... ... ... 1 



Variegated sandstone (viz., red, green, and white), with 15 feet 



of limestone 

 White sands 

 Maffnesian limestone 



46 

 3 

 4 



Total 



650 



1 Rev. C. H. Hartshorne : "A Report on the Drainage of the Nene Valley" 

 Northampton, 1848. 



