568 Proceedings of the Royal Irish Academy, 



LXXYIII. — Ojf THE JorNTrs'& or Eocks ry Eelation' to EifGnraEEiNa, 



ESPECIALLY THE TuX^''ELLIXG OE THE StBAIT OP DoVEK. By PeO- 



PESSOE William Klng, D. Sc. 



[Read, 24t]i Apiil, 1882.] 



PoE some years past having been at different times engaged in study- 

 ing the jointed structure of rocks, ^ I may lay some claim to taking a 

 part in the discussion of a question in Engineering -which public 

 enterprise has lately elevated to a subject of international importance. 



But before proceeding further, I may be allowed to make a few 

 remarks on some points introductory to the subject in hand. 



Already, it may be assumed, the promoters of the proposed 

 Channel Tunnel have had their attention called to the probability 

 that the rocks to be penetrated are so greatly affected by clislocations 

 (faults), and fi-actures of the ordinary kind (that is, resulting from dis- 

 ruption), also to some of them possessing an openly porous character, 

 as to prove serious detriments to the undertaking ; at the same time it 

 must be admitted that some other points of vital importance in sub- 

 marine engineeiing of the kind appear to have been but slightly 

 attended to, or altogether overlooked. 



It is well known that the chalk and immediately associated earlier 

 rocks, in Kent and Sussex, have been flexured into the great elKptical 

 dome, known as the anticlinal of the weald — its longitudinal axis 

 running generally near an east and west course. The consequence is, 

 that the bedding of these rocks variously intersects the horizon from a 

 low angle to a high one. I^ot unfrequently the partings, which 

 define the bedding, are penetrable by water. JN'ow, anyone who 

 has observed the chalk, with the adjoining tertiary sands, clays, and 

 pebble beds, in the Isle of "Wight, standing in a nearly vertical posi- 

 tion, must admit that, if such partings were at the bottom of the ad- 

 jacent sea, the water would necessarily flow into them. It may be 

 doubted that the beds of chalk or other rocks in the Channel are 

 standing at a high angle ; though in some places in the North 

 Downs, notably St. Margaret's, Chapel Hill, they have quite a sudden 

 dip, as mentioned by Hopkins ; but there are no positive grounds for 

 altogether excluding fi'om the line of the tunnel beds lying at angles 

 not exempt from danger : even if their dips be as low as 15°, which is 

 a common figure, bedding partings, it is to be apprehended, would 

 serve as channels for the water to penetrate to the roof, or sides of 

 any submarine excavation. 



Moreover, geologists who have examined the counties under con- 

 sideration have noticed the frequent occurrence in the chalk of " sand 

 pipes" or ''gravel pipes" — large cylindrical openings in a vertical 



^ Transactions of tte Eoyal Irisli Academy, vol. xxt., pp. 605-662 (1875) ; An 

 Old Chapter of the Geological Record (Appendix), pp. 107-119 (1881). 



