THE EXISTENCE OF A FAULT IN THE LIAS NEAR RUGBY. 355 



22. On the probable Existence of a considerable Fault in the Lias 

 near Rugby, and of a new Outlier of the Oolite. By J. M. 

 Wilson, Esq., M.A., F.G.S. (Read April 14, 1875.) 



It may be useful in a future geological survey of Warwickshire if I 

 call the attention of this Society to what seems to me the high pro- 

 bability of the existence of a considerable fault in the Lower Lias 

 near Rugby, which has, I believe, hitherto escaped detection. It 

 is accompanied by an outlier of the Oolite, which is not marked in 

 the maps of the Geological Survey. 



It will be scarcely worth while to give here the detailed tracing, 

 field by field, of parts of this fault. I propose to print these details 

 in the Report of the Rugby- School Natural-History Society, which 

 will be published in a few weeks. It will be sufficient here to notice 

 its probable existence and position, and to invite to it the attention 

 of some competent geological surveyor. 



In the village of Low Morton is a sandpit which is worked against 

 the steep face of a hill to a depth of nearly 50 feet. A few yards 

 from the face of the sand-cliff a well has been sunk 20 or more feet 

 further ; and out in the village, and in the bed of the valley, the 

 sand extends to a greater but still unknown depth. No bottom has 

 ever been reached. In a previous communication of mine to the 

 Society will be seen the account of some borings I made for that 

 purpose *. Above the sand-pit is a clay-pit ; and there is evidence 

 that the clay is bounded on the side towards the sand by a very 

 highly inclined face of clay, against which the sand is thrown. This 

 face of clay can be traced through the ballast-pit by the side of the 

 London and North-Western Railway, having on one side of it deep 

 sand, and on the other clay reaching to within a few feet of the 

 surface. The whole distance within which it can be minutely traced 

 is more than half a mile. 



If this line is continued S.E. it passes close by Kilsby Tunnel, and 

 may be connected with the peculiar difficulties found in the construc- 

 tion of that tunnel from the unexpected inrush of water from large 

 bodies of sand. If continued towards the N.W. it coincides generally 

 with the valley of the Clifton brook ; and its existence is again in- 

 dicated by the great depth of sand in the bed of this valley, which I 

 ascertained by boring, and communicated to the Society. It there 

 passes between Rugby and Brownsover, and is, I suggest, the cause 

 of the existence of the very singular Oolitic deposit on the summit of 

 the Brownsover plateau. There is on this plateau a somewhat ex- 

 tensive Oolitic mass, sometimes rudely stratified, more than 12 feet 

 thick in one place, and quite unmixed with other rock, so as to pre- 

 clude the idea which I once entertained, on a less complete exami- 

 nation of it, that it was an Oolitic drift. At its edges it is much 

 worn with water, and mixed with materials derived from the Lias ; 



* Quart. Journ. Geol. Soc. vol. xxyi. p. 199. 



