[3.8.1] Quidam existimant: Repeating the language that began NQ 3.6.1 to begin a new argument about the source of rivers, namely, the stores of water underground that he has outlined above. This theory of a hollow earth with bodies of large bodies of water inside of it originated in Democritus (Arist. Mete. 365b1-6) and Anaxagoras (Hipp. Refutation 1.8.5). Plato expanded upon it in his Phaedo (111d-112b), an image that appealed to the Roman poets Vergil (G. 4.363-73, and Mynors 1990: ad loc.; A. 6.131-36) and Ovid (Met. 8.562). Lucretius writes of streams and lakes underground to help explain earthquakes (6.536-42), which Seneca will expand upon in NQ 6.8.1. This is ultimately one part of the basic theory that Seneca endorses, in which waters exist under the earth just as above the earth and those underground will supply the terrestrial waters. Areas in Greece, Sicily, and southern Italy are notable for their karst terrain (a geological area of limestone with caves, subterranean streams, and underground drainage). See Ford and Williams 2007 for more on karst landscapes and Clendenon 2009 for full discussion how this topography and various hydrological features were interpreted.
in exteriore parte terrarum: The analogy that the underworld consists of the same features as the outer world is a theory Seneca will repeat elsewhere in this book, see the note infra on NQ 3.16.4: crede infra quidquid vides supra.
vastae paludes: A poetic phrase derived from Catullus (115.5) and Lucretius (5.202). For Catullus such marshlands are a sign of wealth, for Lucretius, an indication that the gods did not make the earth for man. Marshlands and lakes are fresh water so there may also be fresh water underground (cf. aquis dulcibus below). Note how Seneca will linger on the Nile explorers sent by Nero who, when looking for its origins, found inmensas paludes (6.8.4).
ingenti spatio: The vast expanse of the sea is similar to that of the heavens above (sursum ingentia spatia sunt, NQ 1.pr.11.3). Seneca will elaborate on the caverns below the earth with similar language at 3.8.1 and 3.16.4.
infusa vallibus: Corcoran 1971: 220 believes “Seneca appears to be thinking of deep inlets of the sea into the land such as the sea-lochs of Scotland and the bays of S.W. Ireland”. Seneca has the expression also at Dial. 1.1.2 when discussing the laws of the natural world in language that has many commonalities with the NQ (ut infusa vallibus maria molliant terras nec ullum incrementum fluminum sentiant). It is clear that we should assign a late date to De Providentia, cf. Smith 2014: 115-6.
interiora terrarum: Seneca will reuse this phrase when dealing with the temperature of springs at NQ 4a.2.26 and the winds inside the earth (5.14.1).
abundare aquis dulcibus: For more on “sweet” water, cf. 3.2.1 supra. Seneca is repeating abundare from 3.6.2, and the phrase abundent aquis appears at 5.7.2, when discussing breezes that arise from water.
illas late stagnare: The antecedent of illas is aquis dulcibus. stagnare here is intransitive “to lie in pools” (OLD 1), whereas later in this book it is used of the land being covered by flood waters, cf. 3.27.6. Its use here probably reflects the vastae paludes on the surface of the earth as paludes and stagna are connected at 3.30.4. For a similar use of stagnare of the waters under the earth, cf. 5.14.2.
oceanum et sinus eius: The ocean and its bays cover the surface of the earth. These words are connected also at Phaed. 1161-2, when Phaedra seeks to die in a similar way as Hippolytus.
immo eo latius: Seneca corrects this hypothesis by reckoning that the amount of water inside the earth must be more voluminous than that found on its surface. Seneca elsewhere in his prose uses immo with a comparative or superlative in correcting a previous statement, cf. Ep. 92.26: atqui hoc quoque incredibile est, immo incredibilius; Ep. 88.10: non esse feliciorum…immo…infelicissimus. Seneca often employs immo for rhetorical point throughout his works.
plus terra in altum patet: patere here indicates “to extend in space, stretch or spread out” (OLD 7). There is a slight incongruity with this verb as it can also mean “to be open” or “to be visible”, but this land (and water) is invisible to us generally. Seneca repeats in altum from 3.7.3 when discussing wells in order to indicate that far more water can be found the deeper one goes.
ex profunda copia: profunda blurs its primary meanings of “bottomless/inexhaustible” (OLD 1) as well as “situated far below the surface” (OLD 2). copia is used of water at Ben. 7.3.3, NQ 3.11.3, 3.12.1, and 2.26.3. Plato calls this store of water Tartarus at Phaedo 112a.
isti amnes egeruntur: Seneca uses iste to refer to the rivers under discussion with the interlocutor (Lucilius or possibly even the reader). The use of the second-person demonstrative (A&G 297c) adds to the feel that this is a dialogue with Lucilius, cf. 3.pr.8.2, 3.15.1, 3.25.11, for additional moments when this demonstrative has this force.
quid miraris: Cf. 3.4.1 supra for the way in which Seneca counters a possible sense of wonder with the matter-of-fact evidence presented in his doxography. The conclusion of this section mirrors 3.4.1 in language and topic. This should be thought of as purposeful, see Seneca’s defense of such repetition at NQ 2.21.4 and Hine’s observation (2010: 15) “He is fond of saying the same thing twice, even three times, in a slightly different way (e.g., 2.9.4; 6.1.4; more extensively, 4b.11).”
detractos terra non sentit: Slight personification of the earth (cf. 3.4.1), which has been shown in this section to be more extensive than the expanse of waters on the earth’s surface.
cum adiectos maria non sentiant: The truism that the seas do not rise in spite of river water (cf. 3.4.1) is here marshaled in parallel language (terra non sentit/maria non sentiant) to “prove” that the earth will not feel the loss of water.
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