The Roman History · Amm. 23.6.86

And a proof that this produce arises from and is nourished by some aërial derivation rather than by any fattening power in the sea, is that the drops of morning dew when infused into them make the stones bright and round; while the evening dew makes them crooked and red, and sometimes spotted. They become either small or large in proportion to the quality of the moisture which they imbibe, and other circumstances. When they are shaken, as is often the case by thunder, the shells either become empty, or produce only weak pearls, or such as never come to maturity.

Ammianus Marcellinus · translated by C. D. Yonge · 1911 reprint
C. D. Yonge translation (preface dated February 1862); G. Bell and Sons, 1911; Project Gutenberg #28587
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