Method of conducting the Canal Surveys. 25 



terials of a solid and durable character. Its inner edge likewise is 

 usually protected by a slope wall of stone or docking of timber to re- 

 sist the action of the water, the abrasive effects of which if they oc- 

 cur at all, are confined to short distances and to particular places, 

 and under circumstances, which render it an easy matter to deter- 

 mine the precise extent of the encroachment. Upon the New York 

 Canals, and indeed upon most other works of the kind in the coun- 

 try, there are distances of miles together where substantial buildings 

 or bridges or objects of an equally permanent character cannot be 

 found, in consequence of which, and from the little reliance to 

 be placed upon the directive property of the magnetic needle, in 

 tracing long and irregular lines, in cases where an error of even 

 one or two feet in the distance of a mile would be attended with se- 

 rious inconvenience, and considering moreover, the imperfection and 

 disagreement of different instruments, and the want of the requisite 

 skill not uncommon with many surveyors, a constant reference to 

 some part of the Canal, as a standard for preserving the location of 

 the outlines becomes absolutely essential. 



In selecting the part of the Canal for this purpose, the choice, it 

 will be obvious, would necessarily fall, either upon the inner edges of 

 the berm or towing path, or upon one or both margins of the water. 

 Of these the towing path was considered as entided to the preference, 

 since the berm side is not only constructed of less durable materials, 

 more liable to abrasion and seldom kept in proper repair, but for 

 much of the distance where the Canal runs along sidelong ground no 

 regular or artificial berm is formed, the water being allowed to flow 

 back and conform to the natural irregularities of the surface. In 

 some places likewise the berm, is subject to alteration from the grad- 

 ual sliding or giving of the earth producing a contraction of the chan- 

 nel, while the embankment on the side of the towing path remains 

 comparatively firm and undisturbed. Similar objections will like- 

 wise apply to either margin of the water, pardcularly on the berm 

 side, while on both sides the marginal line is subject to constant va- 

 riation from the fluctuations of droughts and floods, and the irregu- 

 lar demand for the supply of inferior levels and for the purposes of 

 lockage. 



From the preceding it will appear, that even in the mode of sur- 

 veying the oudines, as rejected by the commissioners, a general reli- 

 ance must necessarily have been placed, as in the other method, up- 

 on offsets to the inner edge of the towing path, with this difference, 



Vol. XXIV.— No. 1. 4 



