" that all climatal inferences drawn from the number of northern forms in strata containing assemblages of organic remains are fallacious, unless the element of depth be taken into consideration " *.
I mention these observations (made many years since, and which of late have generally been taken into account in all geological inquiries) to show that geologists have still to be guided by the same primary natural-history rules, which have lately received so wide an extension and application in these recent deep-sea dredgings.
The mistake made by Edward Forbes was his assigning the too narrow limit of 1800 feet in vertical depth as the probable zero of animal life in the ocean. Dr. Wallich afterwards extended the probable limits of life to 15000 feet ; and now the important researches of Carpenter, Jeffreys, and Thomson show that it must in all probability be carried very much lower, as they have found a highly organized fauna living in abundance at the vast depth of 14,610 feet, and no indication of an approach to the zero of life. It had, in fact, been long felt that the proposition involved in these bathymetrical limits was open to question.
The many interesting problems connected with the temperature and currents of the ocean have often engaged attention since the early part of this century. It was one of the subjects respecting which a large amount of data was collected on the several scientific naval expeditions sent out by the French Government between 1820 and 1840. Humboldt states† that he showed in 1812 that the low temperature of the tropical seas at great depths could only be owing to currents from the poles to the equator.
D'Aubuisson, in 1819, also attributed the low temperature of the sea at great depths at or near the equator to* the flow of currents from the poles‡.
Lenz§, in 1831, gave the results of some experiments he had made at great depths in the ocean, and concluded that between the equator and 45° of lat. the temperature decreases regularly to the depth of 6000 feet, when the decrease becomes insensible. The lowest temperature he recorded was 36° Fahr.
- Edinb. New Phil. Journ., April 1844.
† Fragmens de Geol. et de Climatol. Asiat. 1831.
‡ Traite de Geognosie, p. 450.
§ Edinb. Journ. of Science, vol. vi. p. 341.
