*[5] Matthew Davidson had been Telford's fellow workman at Langholm, and was reckoned an excellent mason. He died at Inverness, where he had a situation on the Caledonian Canal. *[6] Mr. Hughes, C.E., in his 'Memoir of William Jessop,' published in 'Weale's Quarterly Papers on Engineering,' points out the bold and original idea here adopted, of constructing a water-tight trough of cast iron, in which the water of the canal was to be carried over the valleys, instead of an immense puddled trough, in accordance with the practice until that time in use; and he adds, "the immense importance of this improvement on the old practice is apt to be lost sight of at the present day by those who overlook the enormous size and strength of masonry which would have been required to support a puddled channel at the height of 120 feet." Mr. Hughes, however, claims for Mr. Jessop the merit of having suggested the employment of iron, though, in our opinion, without sufficient reason. Mr. Jessop was, no doubt, consulted by Mr. Telford on the subject; but the whole details of the design, as well as the suggestion of the use of iron (as admitted by Mr. Hughes himself), and the execution of the entire works, rested with the acting engineer. This is borne out by the report published by the Company immediately after the formal opening of the Canal in 1805, in which they state: "Having now detailed the particulars relative to the Canal, and the circumstances of the concern, the committee, in concluding their report, think it but justice due to Mr. Telford to state that the works have been planned with great skill and science, and executed with much economy and stability, doing him, as well as those employed by him, infinite credit. (Signed) Bridgewater." *[7] Letter to Mr. Andrew Little, Langholm, dated Shrewsbury, 16th Sept., 1794. *[8] lbid. *[9] Letter to Mr. Andrew Little, Langholm, dated Salop, 20th Aug., 1797. CHAPTER VII. IRON AND AND OTHER BRIDGES. Shrewsbury being situated in the immediate neighbourhood of the Black Country, of which coal and iron are the principal products, Telford's attention was naturally directed, at a very early period, to the employment of cast iron in bridge-building. The strength as well as lightness of a bridge of this material, compared with one of stone and lime, is of great moment where headway is ofimportance, or the difficulties of defective foundations have to be encountered. The metal can be moulded in such precise forms and so accurately fitted together as to give to the arching the greatest possible rigidity; while it defies the destructive influences of time and atmospheric corrosion with nearly as much certainty as stone itself.