1-12 THE THAMES TUNNEL. 



ground, in the way that the shafts of wells are usually sunk. By this 

 means he succeeded in passing through a bed of gravel and sand 26 feet 

 deep, full of land-water, constituting in part a quicksand, in which the 

 drift makers of the former undertaking had been compelled to suspend 

 their work. 



Being warned by eminent geologists of the existence of a bed of sand, 

 lying at a greater depth, Mr. Brunei caused the fifty feet shaft to be 

 sunk to the depth of sixty-five feet, and a smaller one was made of 

 twenty-five feet diameter, destined to serve as a well or reservoir, for the 

 drainage of the water; this was sunk from the lower level, but on 

 approaching the depth of eighty feet the ground gave way suddenly, 

 sinking the smaller shaft several feet at once, thus proving the existence 

 of the bed of sand before alluded to, and which the active mind of Mr. 

 Brunei had effectually guarded against, and thus succeeded in obtaining 

 the desired level. This accomplished, the shaft and reservoir having 

 been completed, the horizontal excavation for the body of the Tunnel 

 was then commenced at the depth of sixty-three feet, and in order to 

 have sufficient thickness of ground to pass safely under the deep part of 

 the river, the excavation was carried on to a declivity of two feet three 

 inches per hundred feet. This excavation is thirty-eight feet in breadth, 

 and twenty-two feet six inches in height, presenting asectional area of eight 

 hundred and fifty feet, and being more than sixty times the area of the 

 drift which was attempted before. As an illustration of the magnitude 

 of the excavation for the Tunnel, it is larger by sixty feet than the 

 interior of the old House of Commons, and the base of the excavation, 

 in the deepest part of the river, is 76 feet below high water mark. 



We shall now proceed to notice (too briefly, we fear) the process by 

 which this great excavation has been effected, and the double roadway 

 and paths which extend about eight hundred and sixty feet under the 

 River, have at the same time been constructed within it. 



It was accomplished by means of a powerful apparatus of iron, which 

 has been designated a " shield," and which consisted of twelve great 

 frames, standing close to each other, like so many volumes on the shelf 

 of a book-case; these frames being twenty-two feet in height, and about 

 three feet in breadth. They were divided into three stages or stories, thus 

 presenting thirty-six chambers or cells for the workmen; namely, the 

 miners, by whom the structure is simultaneously formed, and which serves 

 as a scaffolding for them. Towards the head and foot of the shield were 

 horizontal screws, a pair of which, being attached to each of the divisions, 



