MEMOIR OF AUGUSTE BRAVAIS. 157 



vatioii of the tides, and having afterward collated his own measure- 

 ments with those executed at Eeikiavik, in Iceland, and Bell Sound, in 

 Si)itzbergeu, by MM. Lottin and Laroche-Poncie, and submitted the 

 M-hole to a thorough discussion, he determined the units of height of 

 tide in several ports of the Xorth Atlantic Ocean. He also calculated 

 for those coasts the value of the semi-diurnal tide and that of the diur- 

 nal tide for both the sua and moon. He was struck witli tlie relative 

 importance which the diurnal tide there assumes, and this circumstance, 

 compared with the analogous fact already observed in the Sea of Kamt- 

 chatka, led him to infer that the tides of the Atlantic and Pacitic 

 mutually influence one another through the Straits of Behring. 



The banks of the Altenfiord, in the environs of Bossekoi) and ITam- 

 merfest, as well as at many intermediate localities, ])resent terraces 

 having almost horizontal surfaces, whose regularity recalls the construc- 

 tions of fortitication, though there is nothing artiticial about them. Each 

 of these terminates at the foot of the rocks in a line marked by erosions 

 similar to those which the sea i)roduces on its present beach. In each 

 terrace is easily recognized an ancient marine coast, on which the sea 

 has beaten for a long time at a well-defined height. At some points 

 several of these are to be seen, one above the other. M. Bravais occu- 

 pied himself in a determination of the actual elevation of all 'tliese 

 traces of the ancient level of the sea, and here botany has furnished 

 him a useful resource. A marine plant, the Fucus vcsiculosus, widely 

 dispersed on those coasts, grows upon the rocks only at a certain dis- 

 tance beneath the mean surface of the sen, and forms a yellowish zone, 

 of which the upper limit is well marked and perfectly horizontal. This 

 line supplied the plane to which M. Bravais referred, by precise level- 

 lugs, the ancient marks of erosion by the sea ; and he thus recognized 

 that all these traces of its ancient altitude form five series, more or less 

 distinct, two of which especially are perfectly unbroken ; that these 

 last are slightly inclined from the interior of the continent toward the 

 ocean, and that one of them in particular ijresents two parts of which 

 the inclinations are difterent. From this we are authorized to conclude 

 that tliese terraces and the ground which supports them have been 

 lifted above the level of the sea ; for, if it were the sea which had sub- 

 sided, each of the two series of terraces would have been perfectly hori- 

 zontal. The mobility of the solid crust of our globe is thereby fully 

 demonstrated. It might be said that the expression, Jirm as a roclc, if 

 taken in too absolute a sense, embodies an illusion, and that there is 

 nothing more unstable in the world than the mean level of the sea. 



M. Bravais was occupied with these subjects till the moment when 

 the corvette, returning from Spitzbergen, again arrived at Hammerfest. 

 The members of the commission then separated for the last time, in 

 order to return to their respective countries by different routes. M. Bra- 

 vais associated himself with M. Martins to return by land, and, still 

 herborizing, traversed, barometer in hand, the plateau of Lapland, 

 where the two travelers determined with precision the altitudes of the 

 upi)er and lower limits of the different zones of vegetation. In this 

 way they completed, not the Atlantic flora of Desfontaines, as M. Bra- 

 vais had seemed destined to do, but the admirable labors in botanical 

 geography of Leopold von Buch and the celebrated flora of Wahlem- 

 berg. 



In the vast forests of Sweden, MM. Martins and Bravais had many 

 opportunities of observing the Pinus silvestris, (Scotch fir,) of which 

 those forests are in great part composed, and published at their return 

 a memoii' on the growth of that tree, a work which had been recom- 



