The Sluice-theory of Strato led Eratosthenes of Cyrene (the most celebrated in the series of the librarians of Alexandria) to investigate the problem of the uniformity of level in all external seas flowing round continents, although with less success than Archimedes in his treatise on floating bodies.[[LS]] The articulation of the northern coasts of the Mediterranean as well as the form of its peninsulas and islands had given origin to the geognostic myth of the ancient land of Lyctonia. The origin of the lesser Syrtis, of the Triton Lake,[[LT]] and of the whole of Western Atlas,[[LU]] had been embodied in an imaginary scheme of fire-eruptions and earthquakes.[[LV]] I have recently entered more fully into this question,[[LW]] in a passage with which I would be allowed to close this note:
“The northern shore of the Mediterranean possesses the advantage of being more richly and variously articulated than the southern or Lybian shore, and this was, according to Strabo, already noticed by Eratosthenes. Here we find three peninsulas, the Iberian, the Italian, and the Hellenic, which, owing to their various and deeply indented contour, form, together with the neighbouring islands and the opposite coasts, many straits and isthmuses. Such a configuration of continents and of islands that have been partly severed and partly upheaved by volcanic agency in rows, as if over far-extending fissures, early led to geognostic views regarding eruptions, terrestrial revolutions, and outpourings of the swollen higher seas into those below them. The Euxine, the Dardanelles, the Straits of Gades, and the Mediterranean with its numerous islands, were well fitted to originate such a system of sluices. The Orphic Argonaut, who probably lived in the Christian era, has interwoven old mythical narrations in his composition. He sings of the division of the ancient Lyctonia into separate islands, ‘when the dark-haired Poseidon in anger with Father Kronion struck Lyctonia with the golden trident.’ Similar fancies, which may often certainly have sprung from an imperfect knowledge of geographical relations, were frequently elaborated in the erudite Alexandrian school, which was so devoted to everything connected with antiquity. Whether the myth of the breaking up of Atlantis be a vague and western reflection of that of Lyctonia, as I have elsewhere shown to be probable, or whether, according to Otfried Müller, ‘the destruction of Lyctonia (Leuconia) refers to the Samothracian tradition of a great flood, which changed the form of that district,’ is a question which it is here unnecessary to decide.”
[79]. p. 217—“Precipitation from the clouds.”
The vertical ascent of currents of air is one of the principal causes of the most important meteorological phenomena. Where a desert or a sandy surface devoid of vegetation is surrounded by a high mountain-chain, the sea-wind may be observed driving a dense cloud over the desert, without any precipitation of vapour taking place before it reaches the crest of the mountains. This phenomenon was formerly very unsatisfactorily referred to an attraction supposed to be exercised by the mountain-chain on the clouds. The true cause appears to lie in the ascent from the sandy plain of a column of warm air, which prevents the condensation of the vesicles of vapour. The more barren the surface, and the greater the degree of heat acquired by the sand, the higher will be the ascent of the clouds, and the less readily will the vapour be precipitated. Over the declivities of mountains these causes cease. The play of the vertical column of air is there weaker; the clouds sink, and their disintegration is effected by a cooler stratum of air. Thus deficiency of rain and absence of vegetation in the desert stand in a reciprocal action to one another. It does not rain because the barren and bare surface of sand becomes more strongly heated and radiates more heat; and the desert is not converted into a steppe or grassy plain because without water no organic development is possible.
[80]. p. 218—“The indurating and heat-emitting mass of the earth.”
If according to the hypothesis of the Neptunists (now long since obsolete), the so-called primitive rocks were also precipitated from a fluid, the transition of the earth’s crust from a condition of fluidity to one of solidity, must have been followed by the liberation of an enormous quantity of caloric, which would have given rise to new evaporation and new precipitations. The more recent these precipitations, the more rapid, the more tumultuous, and the more uncrystalline would they have been. Such a sudden liberation of caloric from the indurating crust of the earth, independent of the latitude, and the position of the earth’s axis, might indeed occasion local elevations of temperature in the atmosphere, which would influence the distribution of plants. The same cause might also occasion a kind of porosity which seems to be indicated by many enigmatical geological phenomena in floetz rocks. I have developed my conjectures on this subject in detail in a small memoir on primitive porosity.[[LX]] According to the views I have more recently adopted, it appears to me that the variously shattered and fissured earth, with its fused interior, may long have continued in the primeval period, to impart to its oxidised surface a high degree of temperature, independent of its position with respect to the sun and to latitude. What an influence would not, for instance, be exercised for ages to come on the climate of Germany by an open fissure a thousand fathoms in depth, extending from the Adriatic Gulf to the northern coast? Although in the present condition of the earth, long-continued radiation has almost entirely restored the stable equilibrium of temperature first calculated by Fourier in his Théorie analytique de la Chaleur, and the outer atmosphere is now only brought into direct communication with the molten interior of the earth, by means of the insignificant openings of a few volcanoes; yet in the primitive condition of our planet, this interior emitted hot streams of air into the atmosphere through the various clefts and fissures formed by the frequently recurring foldings (or corrugations) of the mountain strata. This emission was wholly independent of latitude. Every newly formed planet must thus in its earliest condition have regulated its own temperature, which was, however, subsequently changed and determined by its position in relation to the central body, the sun. The moon’s surface also exhibits traces of this reaction of the interior upon the crust.
[81]. p. 218—“The mountain-declivities of the most southern parts of Mexico.”
The spherical greenstone in the mountain district of Guanaxuato is perfectly similar to that of the Fichtelberg in Franconia. Both form grotesque domes, which break through and are superimposed on transition argillaceous schists. In the same manner pearl-stone, porphyritic schist, trachyte, and pitch-stone porphyry present analogous forms in the Mexican mountains, near Cinapecuaro and Moran, in Hungary, Bohemia, and in Northern Asia.
[82]. p. 220—“The Colossal Dragon-tree of Orotava.”
This colossal dragon-tree (Dracæna draco) stands in the garden of M. Franqui, in the little town of Orotava, called formerly Taoro, one of the most charming spots in the world. In June, 1799, when we ascended the Peak of Teneriffe, we found that this enormous tree measured 48 feet in circumference. Our measurement was made at several feet above the root. Nearer to the ground Le Dru found it nearly 79 feet. Sir G. Staunton asserts that at an elevation of ten feet from the ground, its diameter is still 12 feet. The height of the tree is not much more than 69 feet. According to tradition it would appear that this tree was venerated by the Guanches (as was the ash-tree of Ephesus by the Greeks, the Plantain of Lydia, which Xerxes decorated with ornaments, also the sacred Banyan-tree of Ceylon), and that in the year 1402, which was the period of Béthencourt’s first expedition, it was as large and as hollow as in the present day. When it is remembered that the dragon-tree is everywhere of very slow growth, we may conclude that the one at Orotava is of extreme antiquity. Berthollet says, in his description of Teneriffe, “On comparing the young dragon-trees which grows near this colossal tree, the calculations we are led to make on the age of the latter strike the mind with astonishment.”[[LY]] The Dragon-tree has been cultivated from the most ancient times in the Canary isles, in Madeira, and Porto Santo, and that accurate observer, Leopold von Buch, found it growing wild near Iguesti in Teneriffe. Its original habitat is not therefore the East Indies, as has long been believed; and its appearance does not afford any refutation of the opinion of those who regard the Guanches as a wholly isolated primitive Atlantic race, having no intercourse with African or Asiatic nations: The form of the Dracænæ is repeated on the southern extremity of Africa, in the Isle of Bourbon, in China, and in New Zealand. In these remotely distant regions we recognise species of the same genus, but none are to be found in the New Continent, where this form is supplied by the Yucca. The Dracæna borealis of Aiton is a true Convallaria, the nature of both being perfectly identical.[[LZ]]