1C6 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[May, 



top, or 1,770 yards, or one mile, at the low water line. The exterior 

 slope or inclination, taken below the line of low water has been left for 

 the sea to form, and i>; fonnd to be at from three to four feet horizontal 

 to one foot perpendicular, and in parts rather steeper, but from low 

 water upwards, which lias been set artifically, it is five horizontal to 

 one perpendicular. The inner slope or that ne.\t to the land is nearly 

 two feet horizontal to one foot perpendicular from the base to the top, 

 which is two feet above high water of spring tides, and forty-five feet 

 wide, rising one foot additional towards the centre. In addition to 

 the sea slope above described, by referring to the drawings, it will be 

 seen tliat there is an exterior berne or foreshore thirly feet wide, at 

 the extremity of the east end, fifty feet wide in the centre, and seventy 

 foct wide at the extreme we.-t end. This foreshore, it will be seen, 

 rises from the toe or base of the outer slope to about five feet above 

 low water at its outer extremity, and serves to break the waves before 

 arriving at the main body of the work, and thus diminish their force, 

 and at the same time to prevent the recoil or back stroke of the wave 

 from undermining the toe or base of the slope, and thus rnaking a 

 breach in the body of the work, which at times might otherwise- occur 

 to a certain extent. Towards the centre of the inner slope or face of 

 the Breakwater (see fig. 1.), it will be seen, that there is a small jetty 

 with a double returned head, for the purpose of enabling boats to land 

 under protection. At the western extremity it will be seen that 

 there is a circular head 370 feet diameter, upon which there is to be 

 constructed hereafter a lighthouse, so designed as to throw a com- 

 plete light over the entrance, at the same time to point out the an- 

 chorage, so that vessels entering at night may coiTie to their moorings 

 with the greatest facility, without fear of running foul of any ships 

 which may already be there. The general depth where the Break- 

 water is placed varies from thii ty-six to sixty feet at low water of 

 spring, tides, which generally rise about eighteen feet, and neaps 

 twelve to fourteen feet. The eastern entrance is half-a-mile wide, 

 and varies from six to seven fathoms at low water, and the western, 

 which is the principal entrance, is about half-a-mile wide, and varies 

 from seven to nine fathoms deep at low water spring tides, and the 

 anchorage, where there is fine holding-ground, varies from eight to 

 nine fathoms at low water spring tides. 



The heaviest and most frequent gales come from the southward and 

 westward, and the wind prevails chiefly from the latter quarter about 

 nine months out of the twelve ; and during gales from this quarter, 

 which are very severe, exposed as it is to the uninterrupted reach of 

 the Atlantic and Bay of Biscay, with such a range of sea and such a 

 depth of water, it may readily be conceived that the sea must neces- 

 sarily be very heavy, and require a corresponding degree of strength 

 to counteract its disasterous effects. 



The great mass or body of the work is composed of limestone 

 brought from the quarries of Overton, lying at the mouth of the river 

 Lary, ealhd Catwater, about four miles distant. The stone is raised 

 ill various sized blocks, from one quarter to ten tons and upwards in 

 weight, which are thrown promiscuously into the sea as they are 

 raised from the quarry, in the line of the Breakwater, taking care that 

 the greatest proportion of the large blocks are thrown upon the outer 

 or sea s'ope, and that the whole, large and small, are so mixed to- 

 gether, that the mass may be rendered as solid as possible. In 

 addition to the smallar class of rubble abovementioned, quarry rubbish 

 and lime screenings are thrown down from time to time in order to 

 fill up the smaller cavities. You must observe, that during the pro- 

 gress of a work of this nature, to a certain extent, storms are ex- 

 tremely beneficial, for they serve to wedge and consolidate the whole 

 mass together, much more effectually and in much shorter time than 

 human ait could perform ; and indeed it is desirable not to hurry 

 until the work, as it proceeds, has been consolidated by the sea in the 

 manner above described, — for until this has been effected and sufficient 

 time allowed, it is in vain to attempt, successfully, the erection of any 

 superstructure. As I have already observed, the work commenced in 

 181-2, and continued with considerable activity until 18-24, during 

 whicli period scarcely any storms of consequence occurred, and the 

 great mass of the work had been completed below low-water mark, 

 and ab'Ut half of the superstructure from the eastern end towards the 

 centre had been carried to the full height above high water, and, judg- 

 ing from what had passed, the able and excellent superintendent, the 

 late Mr. Wheatley, one of the most experienced officers in the navy, 

 concluded, that it -was necessary to incur the expense of an outer slope 

 of 5 to I as originally proposed, and considered necessary by the late 

 Mr. Rennie. The great storm, however, of Nov., 1824, completely 

 established the accuracy of Mr. Rennie's calculations, for the sea in- 

 creased the outer slope from 3 a5 to 1, and transferred with the greatest 

 nicety the superfluous rubble from the outer to the inner slope ; the 

 area of the one was nearly equal to the area of the other, making the 

 requisite allowance that the former had become more consolidated by 



time than the latter. In proportion as the work advanced, it was 

 found that the sea became much more heavy towards the western end, 

 and consequently rendered a more solid description of work necessary; 

 I therefore recommended that the surface should be cased with 

 masonry and a foreshore on the sra-side, encreasing in substance and 

 strength as it approached the west end, where the whole from low 

 water to the top is composed of solid masonry, dowelled, joggled, dove- 

 tailed and cramped together, and the foreshore to be regularly set as 

 far as practicable, and using the diving-bell to fuund the lower courses 

 below low water. I also recommended that air or vent-holes should 

 be made on the surface of the casing where requisite, to enable the 

 air compressed by the waves to escape and prevent it from blowing up 

 the covering ; although it was found by Mr. Stewart, the present in- 

 telligent and experienced resident superintendent, that where sufficient 

 time had been given for the rubble below to become consolidated by 

 the sea, and the masonry casing had been carried up solid from lnw 

 water, that the vent-holes were unnecessary. By refoning to the 

 drawings, you will observe that the stones coloured grey represent 

 granite, which being obtained in larger blocks than the limestone, 

 being more tough and not so brittle, has been found to resist the shake 

 of the waves much more effectually. The lower, or footing granite 

 courses, upon which the rest of the superficial casing abuts, are laid 

 horizontally on their beds, the better to resist any lateral thrust which 

 might otherwise result from sliding ; the same may be observed of the 

 middle, or bonding course, which is also of granite. The whole of the 

 three granite courses are dove-tailed together, as well as being lewised 

 and bolted to each other, so that they may resist effectually every 

 shock to which they are peculiarly liable. 



The mortar for the masonry is composed of one part Italian pozzo- 

 lano, one part aberthaw, or Plymouth lime, mixed up with two parts 

 of fine sharp clean freshwater sand, the whole being thoroughly mixed to- 

 gether, triturated under a mortar mill, and worked up with as little water 

 as possible ; this mortar very soon sets, and in a short time becomes 

 as hard as stone. The exterior beds and joints for a few inches in- 

 wards are pointed with the best Roman cement, which has the property 

 of setting directly, which is encreased by using warm water, but then 

 it has the disadvantage of being easily broken and not uniting again, 

 the other being decidedly preferable as soon as it has set. I also recom- 

 mended that a mass of concrete, composed of similar materials as the 

 mortar above described, only using five parts of sand, more or less, 

 according to the position, should be used in the interior of the work 

 to bed the blocks upon, near the level of low water ; this kind of con- 

 crete I have been in the habit of using for many years past in various 

 maritime works with great success, and even below low water, where, 

 if protected and used in masses together so as to prevent the waves 

 from acting upon it until some time after it has been deposited, soon 

 becomes very solid and durable. 



The loose rubble blocks are transported and deposited in their posi- 

 tion in the following manner : — after having been worked in the quar- 

 ries thi y are transported by railways to the quay side, they are put on 

 board of vessels built expres^ly for the purpose. These vessels are 

 ab 'Ut sixty tons burthen and upwards, and have two railways laid 

 parallel to each, which traverse the hold of the vessel from stem to 

 stern, which can be made to open entirely — as the railways approach 

 the stern-port they form an inclined plane, the last part of which is 

 made to revolve upon an axle, with a check to prevent the truck from 

 going ovei-boardwith thestone ; on the deck of the vessel tliere are fixed' 

 powerful crabs or windlasses. The blocks of stone, together with the 

 trucks, are put on board the vessel, ranged in parallel rows on the rail- 

 ways beiore described. The vessel then takes her departure for her 

 st.ition at tl^e Breakwater, the whole of which has been previously 

 marked out with a sufficient number of buoys ; and upon her arrival 

 at the particular spot where stone is required, she is immediately 

 moored to one of the buoys in question. The crew then commence 

 their labours of discharge by heaving up the trucks containing the 

 blocks of stone, by means of the windlasses on deck ; and when the 

 truck arrives at the termination of the inclined plane at the stern of 

 the vessel, its own weight tilts it over, the block of stone is discharged 

 into the sea in its proper place, and the truck remains ; it is tiien 

 placed upon the deck of the vessel, and there left; and in like man- 

 ner each block is successively discharged, until the whole carg.i has 

 been disposed of: this operation, which is extremely simple, is very 

 soi.n completed, seldom occupying above a quarter of an hour or 

 twenty minutes ; the vessel then returns to the quarry for another 

 cargo, and, according to the state of the wind and weather, will make 

 several voyages a day. At times steam-tugs are used to take them to 

 their stations, which saves a good deal of time; but as the wind blows 

 from the westward during a greater portion of the year, they generally 

 sail back to the quarries. In order to ascertain the state of the work 

 below low-water, fi-erjuent sections are taken on the line of the buoys 



