ON DEEP BORINGS. 189 



by the Diamond Eock Boring Company it is, moreover, possible to bring 

 up the rocks passed through in such solid unbroken pieces or "cores" 

 that they are very suitable for geological examination ; this is done by 

 black diamonds being set in a circle in the base of a steel cylinder, to 

 which rods are attached, and which is made to revolve by steam power. 

 The rock is abraded by the diamonds and rises in a solid mass into the 

 interior of the steel cylinder ; when a sufficient length has been bored, 

 (usually 1ft. or 2ft.,) the columnar piece of rock is detached and brought 

 to the surface, then the cylinder is again lowered and the operation 

 repeated. 



The first deep boring ever made in the south-east of England is 

 represented by the central column on accompanying plate, (Plate VI.) 

 It was put down at Kentish Town, in Highgate, a northern suburb of 

 London, about twenty-five years ago, by a company in search of water, 

 and under the advice of Prof. Prestwich. 



All Geologists know that London is built on sands and clays of 

 Tertiary age ; beneath these lies the chalk which rises up to the north, 

 west, and south of the metropolis, forming the Chiltern Hills and the 

 North Downs. Under the chalk is a sandy bed of no great thickness — 

 the Upper Greensand, beneath which is a stiff blue clay, the Gault ; then 

 under the Gault is the bed from which the Hampstead Waterworks 

 Company hoped to get water at Kentish Town, and which is known as 

 the Lower Greensand. However, after passing through 324ft. of Tertiary 

 strata, 645ft. of chalk, and 130ft. of the Gault, the borer entered — not 

 Lower Greensand, as had been expected and hoped — but red and green 

 marls, which we now believe belong to the Devonian formation, thus 

 proving the absence at this point of an immense thickness of intermediate 

 rocks. 



The other four sections illustrated on the plate all represent borings 

 executed within the last two or three years. The boring at Crossness, 

 on the south side of the Thames, near Blackwall, was also made for 

 water ; it has proved the existence at a depth of 1,005ft. of strata very 

 similar to those at the bottom of the Kentish Town section. After 

 examining specimens of these red marls, I could not help, at a meeting 

 of the Geological Society, remarking their great similarity to the Triassic 

 marls of the Midlands, but of course lithological characters are not of 

 high importance, and, as similar beds occur at one or two points in the 

 Devonian rocks, it would seem more probable that they belong to the 

 latter series ; it is certainly remarkable, however, that neither at 

 Kentish Town nor at Crossness did these "red beds" yield any trace 

 of fossils, in which respect they certainly agree well with the 

 Trias. 



The Meux Brewery boring was made at the junction of Tottenham 

 Court Koad and Oxford Street ; here the Palaeozoic rocks were struck at 

 a depth of 1,064ft., and penetrated for 80ft. ; they were red and green 

 shales full of Upper Devonian fossils, and dipping at an angle of 35 degrees, 

 though in what direction could not be ascertained as, of course, the core 

 is turned round many times before being brought up to the surface. 



