VARIOUS TYPES OF BREAKWATERS. 197 



to prevent this flattening of the slope, and to ensure the courses 

 being in close contact with each other throughout. 1 



This system of building sea- works has of late years been 

 adopted for several important structures, and has attracted a 

 good deal of attention. It is, however, by no means new. 

 Sloping blocks of large stone were used at Ardrossan harbour, 

 below low water, early in the present century. The old north 

 pier at Aberdeen was constructed in this manner by Messrs. 

 Telford and Gibb, in the year 1812; and the old east pier at 

 Peterhead was similarly constructed by Telford about the year 

 1820. 



For rapidity of construction, as well as for immunity from 

 sea-risk during construction, and from injury resulting from 

 settlement, this system compares very favourably with other 

 methods of building breakwaters of the vertical type. 



BREAKWATERS OF THE MOUND TYPE. 

 A. Mound Breakwaters of Rubble Stone. 



It has already been stated (Chap. VIII.) that the materials 

 readily available for a work must always largely influence an 

 engineer in determining its design. This is, perhaps, in no case 

 truer than when applied to the rubble mound type of break- 

 water, inasmuch as no engineer would think of suggesting such 

 a design unless there were an abundant and easily accessible 

 supply of suitable stone in the vicinity. 



In the chapter on "Tides," it was shown to how great an 

 extent breakwaters of this class are influenced by range of tide ; 

 it is, therefore, now only necessary to recall the fact to mind. 

 Indeed, a perusal of Fig. 12, p. 59, will convey more information 

 on the subject than anything further I could say. 



A mound of rubble stone deposited in the sea will, ere 

 long, be washed down by the action of the waves, and it will 

 assume a profile which will vary in form in different localities, 



1 This flattening of the slope is to some extent caused as follows : In heavy 

 seas there is often a perceptible movement of the blocks, which, although it may be 

 exceedingly small, is sufficient to make them rub and chafe one against the other. 

 Small irregularities on their surfaces are thus ground off, and the blocks, pivoting 

 on their bases, fall closer together. In construction, it is, moreover, impossible to 

 make the lower blocks lean so hard against the previous course as the upper ones do. 



