They gather up the elements of the previous philosophies, which they put together in a new form. Their great diversity shows the tentative character of early endeavours to think.
in the Phaedrus, Phaedo, Republic; to which may be added the criticism of them in the Parmenides, the personal form which is attributed to them in the Timaeus, the logical character which they assume in the Sophist and Philebus, and the allusion to them in the Laws.
They relate to a subject of which Plato himself would have said that 'he was not confident of the precise form of his own statements, but was strong in the belief that something of the kind was true.' It is the spirit, not the letter, in which they agree--the spirit which places the divine above the human, the spiritual above the material, the one above the many, the mind before the body.
On the other hand, the ancient and mediaeval logic retained a continuous influence over it, and a form like that of mathematics was easily impressed upon it; the principle of ancient philosophy which is most apparent in it is scepticism; we must doubt nearly every traditional or received notion, that we may hold fast one or two.
The teaching of Spinoza might be described generally as the Jewish religion reduced to an abstraction and taking the form of the Eleatic philosophy.
Not only the grand features in the structure of barrier-reefs and of atolls, and to their likeness to each other in form, size, and other characters, are explained on the theory of subsidence -- which theory we are independently forced to admit in the very areas in question, from the necessity of finding bases for the corals within the requisite depth -- but many details in structure and exceptional cases can thus also be simply explained.
In all reefs, owing to the sediment being washed out of the lagoon-channel to leeward, that side is least favourable to the long-continued vigorous growth of the corals; hence dead portions of reef not unfrequently occur on the leeward side; and these, though still retaining their proper wall-like form, are now in several instances sunk several fathoms beneath the surface.
These latter reefs have been formed whilst the land has been stationary, or, as appears from the frequent presence of upraised organic remains, whilst it has been slowly rising: atolls and barrier-reefs, on the other hand, have grown up during the directly opposite movement of subsidence, which movement must have been very gradual, and in the case of atolls so vast in amount as to have buried every mountain-summit over wide ocean-spaces.
Authors have noticed with surprise, that although atolls are the commonest coral-structures throughout some enormous oceanic tracts, they are entirely absent in other seas, as in the West Indies: we can now at once perceive the cause, for where there has not been subsidence, atolls cannot have been formed; and in the case of the West Indies and parts of the East Indies, these tracts are known to have been rising within the recent period.
 The large claws or pincers of some of these crabs are most beautifully adapted, when drawn back, to form an operculum to the shell, nearly as perfect as the proper one originally belonging to the molluscous animal.
Lyell, even in the first edition of his "Principles of Geology," inferred that the amount of subsidence in the Pacific must have exceeded that of elevation, from the area of land being very small relatively to the agents there tending to form it, namely, the growth of coral and volcanic action.