a. [ad. late L. abyssāl-is of or belonging to an abyss, f. abyss-us; see ABYSS and -AL 1.] Of unsearchable depth, unfathomable; belonging to the lowest depths of ocean. Abyssal zone, the bottom strata of the sea, the belt of water below 300 fathoms.

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1691.  Behmen, Theosoph. Philos., 42. Whose immensity is Abyssal.

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1752.  W. Law, Spir. of Love (1816), II. 66. God is an abyssal infinity of love, wisdom, & goodness.

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1830.  Lyell, Princ. Geol. (1875), II. III. xlix. 589. The Coral fauna of the deep and abyssal sea.

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1872.  Nicholson, Palæont., 23. The abyssal mud of the Atlantic is to a very large extent composed of the microscopic shells of Foraminifera.

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