ENCLOSING DAMS. 



iron, 3 inches by \, welded up in one length, and housed into 

 grooves cut in the centres of the abutting faces. The dam was 



C2' 



SECTION AT A. B. 



SCALE FOR SECTION 

 o s i 15 20 FEET 



^ / / - 



CEB 



FIG. 26. 



FIG. 25. 



strengthened on the inner side by single-pile buttresses, 

 projecting about 10 feet from the inner face. 



Shield. The following is 

 a description of a very in- 

 genious dam or shield (Fig. 

 26) designed by Mr. H. Law, 

 and used by him in con- 

 structing the entrance of 

 a graving dock at Rio de 

 Janeiro. 1 The shore being 

 bare granite rock, an ordi- 

 nary coffer-dam of piles 

 would have been impossible. 

 The site of the proposed en- 

 trance was enclosed with a 

 shield of timber, the bottom 

 of the shield being cut to the shape of the rock against which 

 1 M.P.LC.E., vol. li. f 157. 



