452 Naiural-ttistoficdl Collections. 



These Alga, sometimes of a prodigious length, when torn from their retreats 

 by cuiTcnts or by violent tempests, may become points of recognition to naviga- 

 tors uncertain of their position. They are for them so many notices scattered up- 

 on the surface of the seas, which would inform them not only of an approach to 

 land, but in what country they are ; for different and very distant countries do 

 not generally produce the same Algae. 



In the Austral hemisphere pyriferous Macrocystes announce Magellan's 

 Straits, the Trumpet Varec signalizes the Cape of Good Hope, the elegant Cys- 

 tosira trinodis, and its companion, the Cystosira moniliformis, equally inform 

 us of an approximation to the shores of New Holland ; lastly, in the seas which 

 surround the islands of Newfoundland, of St. Peter, and of Miguelon, so often 

 hidden in dense fogs, the navigator will know that he has arrived on a rocky coast, 

 when he observes a large Laminaria, with an arborescent frond, ornamented late- 

 rally with folds, like so many festoons. The tubular foot of this plant, which I 

 have called Laminaria longicrioris, furnishes a tubular swelling, by the aid of 

 which it floats on the surface of the sea, while the large leaf in which it termi- 

 nates, descends and gradually buries itself in the water, curving round in the form 

 of an arc — Extract from a Flora of Newfoundland and of the Islands of St. 

 Peter and of Miguelon, by M. de la Pylaie. 



On the Forms and Relations of Volcanoes, from the Observations of Leopold 



de Buck ; by Mr, Elie Beaumont The manner in which the effused oi 



upraised craters have been formed, appears to be at the present day one of the 

 principal problems of geology. Its solution, which can only be obtained by the 

 means proposed by Mr. Elie Beaumont, by a study of the forms and relations of 

 volcanoes, would immediately give the key of volcanic phenomena, and would pro- 

 bably also lead us to find that of a much more important phenomenon — the up- 

 raising of chains of mountains. De Buch first pointed out the fact, that in coun- 

 tries where all the rocks present more or less completely the characters of volcanic 

 products, many cavities which have the form of craters, have never been craters of 

 eruption. The oxidated crust of the earth has been elevated by the action of an 

 internal power ; a crater of effusion, (cratere de soulevement,) has been formed, but 

 no permanent canal of communication has established itself in this opening be- 

 tween the interior of the globe and the surface. The volcanic action which has 

 produced this imperfect volcano often makes way at a short distance, giving birth 

 to little craters of eruption, as on the island of Palma, which are generally on a 

 strait line which passes through the centre of the crater of effusion. 



There is a connexion, but not an identity, between the causes of the mechanical 

 action which produced the craters of effusion, and those which continue to sustain 

 volcanic phenomena. There can be no doubt, from the discovery of primitive blocks 

 in the cleft which gives access from Caldera to the island of Palma, that the me- 

 chanical action which produced the craters of effusion developed itself beneath the 

 primitive rocks. It was already known, from the time of Dolomieu, that the 

 seat of volcanic eruptions was also placed beneath the same rocks. 



Craters of eflTusion have seldom been produced in an isolated manner ; on the 

 contrary, many have formed themselves in the neighbourhood of one another, 

 either by grouping themselves around a central and principal volcano, or form- 

 ing themselves in a line whose direction is in relation to the great accidents of the 

 soil of the country. These centres of eruption thus grouped, are not independent 

 of one another. The periods of eruption may be the same or different ; and by 

 comparison of the catalogue of eruptions, we find that Vesuvius, ^tna, and Strom- 

 boli are not only distinct volcanoes, but belong to separate groups, while the vol- 

 canic phenomena of the Canary Islands depend on one another. Each of the 

 Canary Islands, nevertheless, consists of a central crater of effusion of a consider- 

 able diameter, on whose external ridges basaltic columns or fuzes rise on all 

 sides. These islands cannot be the fragments of a great continent. They are a 

 re-union of islands which have been elevated, the one beside the other, and in an 



