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pass under, and be carried to the shaft in Vine Street. Allowing for any likely greater depth of a former channel, or for any effect the river might have had on the clay, Mr. Barlow considered he would be safe in allowing a minimum thickness of 20 ft. of London Clay to exist between the river and the top of the tunnel—a conjecture, the correctness of which has been fully proved in the execution of the tunnel; for not the slightest percolation of water from the river was detected during any part of the work. It is a question, in fact, whether a less depth might not have sufficed. Greater difficulties were apprehended in the making of the two shafts, as the gravel on either side of the river was known to be charged with water—that on the Middlesex side especially. On the north side of the river the ground rises at Tower Hill, and thence towards the City, to a height of about 40 ft. above Thames high-water mark; and the London Clay is capped by a thick bed of gravel, the spring at the base of which supplies so many of the City pumps. This gravel, however, does not slope down to the river, but is cut off at the sloping ground. When the shaft on the north side came to

Fig. 1

be made, it was found, after passing this 14 ft. of made ground, that the site of it was exactly on this intermediate hill of clay, and that the gravel which thinned out only a few feet higher had therefore been escaped. The shaft consequently was carried without difficulty through the 14 feet of made ground and 44 feet of London Clay to a depth of 58 feet. On the south side, the gravel, alluvial, and made soils, a, were found to be 35 feet thick, and charged with water, which rose and fell with the tide (highest just before low water) in the river, to the extent of 3 feet. By the use of iron-tubing, a passage through has been effected, althoughwith more difficulty, and the shaft carried to a depth of 17 feet in the clay b, or a total depth of 52 feet. Between these two points Mr. Barlow laid the tunnel at a slight curve, so as to have a depth in the centre 18 feet greater than at the ends. The shafts have a diameter of 10 feet at top and 8⁠1/2⁠ feet at bottom. The tunnel is 7 feet in diameter, and is formed by cast-iron tubing in lengths of 1⁠1/2⁠ feet each, each ring being composed of thin segments with a key piece. An iron shield, devised by Mr. Barlow, was pushed on in advance of the work, and the tubes fixed in as soon as the requisite length of excavation had been completed, and the small space left between the clay and tube filled in at once by concrete. The work was carried on day and night, and advanced without interruption. No subsidence occurred in any part, and a regular and steady progress of 9 feet daily was made. Mr. Barlow, junior, is the engineer of the work, and Mr. Greathead the contractor; and the whole plan and execution of the work does very great credit both to the projector, Mr. Barlow, and to the engineer and contractor. With the exception of a slight leak in the iron tubing of the shaft on the south side, and which has been remedied after but a short delay, not the slightest mishap has occurred in the execution of the work, nor has a single fatal or even serious accident happened to any of the men. Last month the junction between the north and south side was effected, and the error of direction from the two ends was found not to amount to one inch. The passage under the river will be made in an omnibus, by means, probably, of a stationary engine; and lifts on either side will take the passengers up and down. A few minutes will suffice for the journey, and it is hoped that the work may be opened to the public in a few weeks. A remarkable feature of this interesting work has been its small cost. Mr. Barlow's estimate was 16,000l., and it is now tolerably certain that the entire cost will be under 18,000l. Another feature has been the rapidity of execution. The shaft on the north side was commenced on the 16th of February last. On the 26th of April the tunnel, which is 1,320 feet long, was commenced, and on the 8th of October the passage under the river was safely effected. Before the public at large was aware that another Thames Tunnel was completed, the old London wonder has been duplicated.

As the object has been chiefly to speak of the geological problem, a section is annexed to show the structure of the ground at this part of the river.

Fig. 2

Very few fossils were found, and these chiefly in the clay of the north shaft. They consist of Cryptodon angulatum, Corbula globosa, Pinna affinis, Dentatum nitens, Fusus, and column of Pentencrinite. In the tunnel pieces of wood pierced by the Terredo, and some teeth of Shark, were met with. As the London Clay thickens to the west and north-west, and extends uninterruptedly to Windsor on the one hand and to Watford on the other, covered in places near London by beds of gravel and sand, which never, however, exceed thirty to forty feet in thickness, and rarely exceed fifteen feet, there is thus in this area a formation which lends itself singularly well to the construction of subways and tunnels.

M. FATIO'S book is one which will be valuable to all Swiss naturalists, and to those who take an interest in the productions of the mountainous region of central Europe. It fulfils its function admirably as far as it goes, but, like all works treating of local Faunas or Floras, its general interest is diminished in proportion to the diminution of the area investigated. It has not, for example, the importance or value to a distant reader which such a volume as the "Naturgesch. der Säugethiere Deutschlands und Mitteleuropas" of Blasius possesses; but to local natu-