FORMATION OF REEFS. 71 



But on land, there is the decay of the year and that of old age 

 producing vegetable debris : and storms prostrate forests. And 

 are there corresponding effects among the groves of the sea? 

 It has been shown that coral plantations, from which reefs pro- 

 ceed, do not grow in the "calm and still" depths of the ocean. 

 They are to be found amid the very waves, and extend but little 

 below a hundred feet, which is far within the reach of the sea's 

 heavier commotions.* Here is an agent which is not without 

 its effects. The enormous masses of uptorn rock found on many 

 of the islands may give some idea of the force of the lifting 

 wave ; and there are examples on record, to be found in various 

 Treatises on Geology, of still more surprising effects.f 



* During the more violent gales, the bottom of the sea is said, by different au- 

 thors, to be disturbed to a depth of three hundred, three hundred and fifty, or even 

 five hundred feet, and De la Beche remarks, that when the depth is fifteen fathoms, 

 the water is very evidently discolored by the action of the waves on the sand and 

 mud of the bottom. In the Comptes Revdas, t. xii, 774, M. Siau mentions that par- 

 allel ridges are formed on the bottom, by the motion of the water, which may be 

 readily distinguished at a depth of at least twenty meters. The hollows between 

 such ridges or zones are occupied by the heavier substances of the bottom. Similar 

 zones were distinguished at a depth of one hundred and eighty-eight meters, to the 

 Northwest of the St. Paul's Roads. 



f Lyell, vol. ii, p. 38-40. Speaking of the force of waves on coasts, Lyell men- 

 tions the transportation of a block of stone, ninety feet from its bed, which was 

 eight feet two inches, by seven feet, and five feet one inch in its dimensions, and 

 another nine feet two mches, by six and a half feet, by four feet, having been " hur- 

 ried up an acclivity to a distance of one hundred and fifty feet." 



In an article on the subject, by Thomas Stevenson, of Edinburgh, published in 

 the Transactions of the Royal Society of Edinburgh, (voLxvi, 1845,) it is stated, as a 

 deduction from two hundred and sixty-seven experiments, extending over twenty- 

 three successive months, that the average force for Skerryvore, for five of the sum- 

 mer months, during the years 1843, 1844, was six hundred and eleven pounds per 

 square foot ; and for six of the winter months of the same year, it was two thou- 

 sand and eighty-six pounds per square foot, or three times as great as during the 

 summer months. During a westerly gale, at the same place, in March, 1845, a pres- 

 sure of six thousand and eighty-three pounds was registered by Mr. Stevenson's dy- 

 namometer, (the name of the instrument used.) He mentions several remarkable 

 instances of transported blocks. One of gneiss, containing five hundred and four 

 cubic feet, was carried by the waves five feet from the place where it lay, and there 

 became wedged so as no longer to the moved. Of the manner in which it was 

 moved, Mr. Reid (as cited by Mr. Stevenson) says : " The sea, when I saw it striking 

 the stone, would wholly immerse or bury it out of sight, and the run extended up 

 to the grass line above it, making a perpendicular rise of from thirty-nine to forty 

 feet above high water level. On the incoming waves striking the stone, we could 

 see this monstrous mass, of upwards of forty tons weight, lean landwards, and the 

 back -run would uplift it again with a jerk, leaving it with very little water about it, 

 when the next incoming wave made it recline again." 



Mr. Stevenson states also that the Bell Rock Lighthouse in the German Ocean, 

 though one hundred and twelve feet in height, is literally buried in foam and spray, 

 to the very top, during ground swells, when there is no wind. On the 20th of No- 

 vember, 1827, the spray rose to the height of one hundred and seventeen feet above 

 the foundations or low water mark ; and deducting eleven feet for the tide that 

 day, it leaves one hundred and six feet, which is equivalent to a pressure of nearly 

 three tons per square foot. 



With such facts, any incredulity respecting the power of waves should be laid 

 aside. Moreover, it may be remarked that the Pacific is a much wider ocean than 

 the Atlantic, with far heavier waves in its ordinary state. 



