The first Spanish inhabitants entertained a thorough belief that the province of Guayra was rich in metals; and there too, they promised themselves to find abundance of precious stones. They had not yet learnt that all that glitters is not gold nor diamonds either. On the shores of the Parana, they found some stones which they called _cocos de mina_. These stones in shape are sometimes round, sometimes oval; their surface is rough and hard, and of a dark colour. In size they are equal to a pomegranate, and sometimes to a man's head. Within the outer shell they contain little stones of various colours, and great value in the eyes of ignorant persons, who take them for crystal, amethysts, rubies, emeralds, &c. But they are deceived. Jewellers rate them about as high as Bohemian stones. They say that the _cocos de mina_, pregnant with these kinds of pebbles, burst with a noise as loud as that of a gun, when what they consider the noble burden which their womb contains is mature. This appearance and these properties are attributed to them by the vulgar, with what truth I know not, for though I have travelled over the greatest part of Paraguay, particularly the shores of the Parana, with eyes attentive to nature, I never saw a stone of this kind. I do not pretend to say that the _coco de mina_ may not have its value in the other provinces of America, which produce genuine jewels, but I boldly deny that any inhabitant of Paraguay was ever enriched with one. The foolish credulity of certain persons, who, from this fallacious resemblance of jewels, hoped to gain riches, was punished with extreme poverty, as we all know. Xerez, Ciudad Real, and Villa Rica, cities formerly accounted fountains of metals and of riches, have all proved seminaries of indigence and misery. What was called Villa Rica, or the Rich City, was never opulent in reality, but only so in name, and the hopes it held out of discovering metals.