Nothing but preaching.
Of the stone called mermecoleon. There is a stone in the sea which is called in Latin mermecoleon and in Greek concasabea, because it is both hollow and round. It is, moreover, divided into two parts, so that if it wants to, it can close up. The stone lies at the bottom of the sea and comes to life early in the morning. When it rises from its resting-place to the surface of the sea, it opens its mouth and takes in some heavenly dew, and the rays of the sun shine around it; thus there grows within the stone a most precious, shining pearl indeed, conceived from the heavenly dew and given lustre by the rays of the sun. The stone, therefore, is called conchus; it symbolizes Saint Mary, of whom Isaiah foretold, saying: ‘There shall come forth a rod out of the stem of Jesse’ (Isaiah, 11:1). And again: ‘Behold a virgin shall conceive and bear a son’ (Isaiah, 7:14). Of the rod and the virgin, Saint Mary, it is said: ‘A flower was born of Saint Mary, our Lord Jesus Christ’. For just as the stone rises from the sea, so Saint Mary went up from the house of her father to the temple of God and there received the dew from heaven. These are the words which were said to her by the archangel Gabriel: ‘The Holy Ghost shall come upon thee, and the power of the Highest shall overshadow thee; therefore also that holy thing which shall be born of thee shall be called the Son of God’ (Luke, 1:35). Behold these words are the heavenly dew, just as before her, the patriarch Isaac, blessing his son, signifying that Christ would be born from his seed, said to him: ‘God give thee of the dew of heaven and the fatness of the earth’ (Genesis, 27: 28), signifying the chaste, untouched virgin Mary. ‘Early in the morning’ refers to the time of prayer. The mussel opening its mouth signifies the occasion when Mary says to the angel: ‘Behold the handmaiden of the Lord; be it unto me according to thy word’ (Luke, 1:35).