1S40.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



167 



m.irble. The external surface of the shell is rough, auil radi^ited 

 transversely and longitudinally in a most Ijeautiful luauucr by curved 

 lines of a high order; an attentive study of the mere lined surface of 

 the shell cannot fail to be instructive even to tlie man of science, and 

 worthy to be contemplated and examined by all those engaged in the 

 works of art and taste. The marine engineer may derive instruction 

 from the parabolic curves delineated, and traced out by the hand of 

 nature on the Fholas shell, in assisting him in giving the best shape 

 to the slopes of breakwaters, and harbuiu-s constructed in the deep sea, 

 and exposed to the run or momentum of the ocean. The curved ra- 

 diation or fluting on the shell cannot fail to attract the architect 

 engaged in the works of design and taste. It ought not to be forgotten 

 what struck Watt in examining the joints in the tail of a lobster ; nor 

 of .Smeaton in looking at the form of an oak tree ; nor the falling of an 

 apple which gave the impulse to the genius of a man justly the glory 

 of our island, and whose name stands recorded with the jiroudest 

 triumphs in the loftiest branches of science that has yet adorned the 

 efforts of human ingenuity. 



William Bald. 



ENCROACHMENTS OF THE SEA AND FORMATION OF 

 SHORES. 



Sir — Public attention has of late years been mncli engaged by the 

 phenomena observed upon the ocean. The tidal theory, currents, 

 storms, &c. have each been subject to the closest scrutiny, and the re- 

 sidt has been much valuable information connected with them. The 

 recovery of land, and the encroacliment of the sea, liave been for some 

 time, and are now subjects of great interest to the scientific world ; 

 this has induced me to request the insertion of tlie following few lines 

 in the columns of your valuable journal. 



The northern shore of the Bristol Channel from the port of Cardiff 

 up to Gloucester consists of a vast flat of Moor land, varying from 1 to 

 1^ miles in breadth; the soil is composed of a very tenacious clay 

 mixed with shells and a large portion of decayed vegetable matter. 

 This tract is formed totally from the deposit of the waters of the 

 Severn and Bristol Channel. This fact is inferred from the following 

 circumstances: — -Ist. The soil above described commences about a 

 mile and a half inwards, where its section presents a depth of about 

 a foot, under which is fovmd the natural soil of the country, a yellowish 

 clay intermixed with gravel; from this point it gradually deepens to 

 high water mark, where the depth averages from 35 to iO feet. 2nd. 

 If a plate or any other body, having a flat surface, be exposed on the 

 shore, between high and low water marV, for a single tide, a deposit 

 will be found thereon varying in thickness according to the calmness 

 of the sea during tide, as it has been observed that tlie deposit is much 

 increased in stormy wheather when the sea is violently agitated. 3rd. 

 In excavating the Bute Docks the rudder of a sliip was found about lU 

 feet below the surface, the iron work of which was in excellent pre- 



Fig. 1. Fig. 2 



r 

 I 



! 



I 



I- 



I ^=s?^^; ,,5.,^— i— — — ^^ 



I ^■-— i 



I 



I 



H ^ 



I 



Pig. 3. 



Fi". 1 , the length of the upper ordinate is G feet, the second G feet 3 inches, 

 (he third 6 feet, the fuurtli 5 ieet 1 inch, an 1 the height of the vertical line 

 5 feet 9 inches. Fig 2, length of the upper ordinate 2 leet 11 inches, th',' 

 second 3 feet 3 inches, the thiid 3 feel 2 inched, and the length of the vertical 

 line 5 feet. Fig. 3, length of the upper ordinate is 3 feet 8 inches, tbesecund 

 '.') feet 9 inches, the third 4 feet, the fourth 3 feet 7 inches, and the length of 

 the vertical line 5 feet 5 inches. The lower line is the height of high water 

 and spring tides. 



servation. It was at first supposed that it liad sunk down by its own 

 weight, but its peculiar shape, and the closeness and tenacity of the. 

 soil, at once indicate the fallacy of such an opinion; several oak trees 

 were also founrl about 311 feet below the surface, and about lUO yards 

 above high water mark, these were of sufficient hardness to admit of 

 their being worked up into chairs, boxes, &c. 



These facts, I presume, fully warrant my assertion that the shore i.s 

 a deposit, and if so, it only remains to discover the cau^e, which ap- 

 pears to ine to be as follows : — hi many seasons when the Severn is 

 swollen into a most impetuous and rapid torrent, vast quantities of the 

 rich soils of Hereford, Gloucester and Worcestershire are washed down 

 by it, and the particles prevented from sinking by the rapidity of the 

 current, they are thus carried along until the stream is impeded in its 

 progress by meeting the flowing tide, which runs in this channel with 

 a velocity of from .) to (J miles an hour; the tide being the more 

 powerfid of the two currents, and having a set towards the south-east, 

 pushes the other current over towards the nothern shore, wliere the 

 water almost stagnates and the particles settle to the bottom. I am 

 borne out in this opinion by the fact that there is but little current in 

 the space between high and low water mark, a distance of about a 

 mile, and wluch always sets to the westward whether the tide be ebb- 

 ing or flowing. 



At the high water mark the shore suddenly drops about six feet 

 perpendicularly, the profile of the land at this part is exceedingly 

 curious, and accompanving this paper I have sent a few sections taken 

 at the more prominent parts, and consequently most exposed to the 

 force of the wave. I think some very valuable hints might be taken 

 from them in the construction of piers, sea walls, and other works ex- 

 posed to the action of the sea. These sections were taken with mucli 

 care, and may be fully relied on for accuracy. 



I remain your most obedient servant, 



NOTA. 



EN'CRO.\CmiENT,S AND RECESSIONS OF THE SEA. 



[The following article is from the Ciiujue Ports Chronicle of February last, 

 it is a reply to a paper which appeared in the Journal, page 04, for Feliniary 

 last, under tlie signature E.] 



■\Ve regret that " E," while he questions the accuracy of our theory, has 

 not started some taugiljle objection for us to grapple with, and as he has not; 

 done this, we must content ourselves witli a reference to some additional 

 facts in corroboration of the \"iew we hold of the stdiject. "We find that as 

 the projections of the Hastings clift's are diminished, additional deposits of 

 beach are fonued in the West bay, gradually augmenting also at Dungeness 

 Point, the extremity of the cm've described by the sea, on account of the 

 land, though low, consisting, wc believe, of chalk or other formatiuii, calcu- 

 lated to resist the action of the waves. It is also a fact that, as the Ness 

 point augments to seaward by deposits of beach, the sea has receutly made 

 considerable encroachments to the eastward, or side opposed to the prevail- 

 ing current. M'ithin the last few days also, a temporarj' headland has been 

 caused about one mile s.w. of Dover, by the fall of an immense quantity of 

 chalk, denominated Round-down CUff. Now by obstructing the parallel 

 course of the western current, it woidd, according to our theory, throw the 

 tide in with additional momentum upon the weslern pier of Dover harbour, 

 and this, we believe, has since been reahzed, and so eti'ectually as to diminish 

 the bar of Ijeach, which, for some months previously to this accident, had 

 been collecting in serious and unusual quantities. Nature has thus, we con- 

 ceive, by one of her accidents, demonstrated the means, which our celebrated 

 engineers have hitherto searched for in vain, of preventing the formation of 

 a bar of beacli at the mouth of Dover harbour. Viewing that locaUty in 

 connexion with our theory, we have no doulit that if masses of rock, forming 

 a duraljlc obstruction in tlie nature of a headland, were deposited at a proper 

 distance from the entrance of the harbour, the artificial promontory would 

 give such a curviUnear and additional impetus to the waves and current, as 

 would tend to pass tlie beach lieyoud the east pier of the harboiu:. 



Tlie recent south-westerly gales have, however, contributed events under 

 our immediate observation which, in our humble opinion, have triumphantly 

 established the theory we have Ijroached, and wliich " E " has not attacked 

 on any specific point. The circumstances to which we allude are the follow- 

 ing : a groyne was constructed some few months ago on the beach a little to 

 the westward of the villas between Verulam Place and Warriors' Square, for 

 the purpose of protecting the esplanade wall to the eastward. That it ef- 

 fected by retaining the beach, which effectually repels the inroads of the 

 waves. Here, then, we had a promontory formed on a miniature scale, and 

 it was not long before what we conceive to bo tlie great lav/ of nature, viz., 

 the formation of a 'lay exactly proportioned to the obstruction caused to the 

 sea by an intervening headland, became too apparent. Tiie waters, inter- 

 rupted ill their course by the beach collected at the groyae, were thrown 

 witli an additional impetus to the eastward of the groyne, exactly, we beheve, 

 proportioned to the obstruction they had encountered, aii.l after repeated 

 assaults upon tlie wall, have undermined, washed if, the parade, and part of 



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