. Railway age . of rock, and the comparatively small dimensionsof the work in question. The shield was placed in Its flrst iwsltlou at the bottom of theshaft by the first of January, 1826, and the structure of the doublearchway of the tunnel was i-ommenced under a bed of clay; buton the 2Bth of the same month the stratum of clay was discoveredto break off ;ibrui>ily, li\ivini; the shield for upwards of six weeks Cross Section of Tunnels. bed of the river, increasing daily In its progress. By the 13thof April, 1827, the tunnel had extended 400 ft. under the river;these 400 ft. of the tunnel
. Railway age . of rock, and the comparatively small dimensionsof the work in question. The shield was placed in Its flrst iwsltlou at the bottom of theshaft by the first of January, 1826, and the structure of the doublearchway of the tunnel was i-ommenced under a bed of clay; buton the 2Bth of the same month the stratum of clay was discoveredto break off ;ibrui>ily, li\ivini; the shield for upwards of six weeks Cross Section of Tunnels. bed of the river, increasing daily In its progress. By the 13thof April, 1827, the tunnel had extended 400 ft. under the river;these 400 ft. of the tunnel were excavated, and the double arch-ways sul»stantially completed with brick-work In ten months anda half. On the 18th of May, 1827, and again in the month of Jan-uary, 1828. the river broke in, and filled the tunnel; thereby occa-sioning the apprehension that this unprecedented undertaking,which had excited so much interest, not only in England, butthroughout Europe, might be abandoned. After, however, filling. Frame of Shield. the chasms in the bed of the river with bags of clay, and clearingthe tunnel of water, ui)on re-entering it, the structure was found Ina perfectly sound and satisfactory state; and the strongest proof isa^orded of the efflclency of Mr. Bruneis system of constantly pro-lectiitg as much as possible every part of the soil during the exca-vation; and finishing tho structure in the most solid manner as thework proceeded, by the instrumentality wholly of the shield. Subs<Hiuent to these eruptions of the river, such was the desire May 22, IflOS. THE RAILROAD GAZETTE. 703 to see the work completed that several hundred plans were commu-nicated to the directors and engineer tor filling up the cavity, aswell as for the prevention of future accidents. All the plans wereduly examined, and attentively considered; and the board of direc-tors , under date of the ICth of December, 1828, their obli-gations to the many scientific men who had so spontaneously
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