And beginning, we first examined the black stones. And such as they had been taken out of the building, were they found to remain; and the Shepherd ordered them to be removed out of the tower, and to be placed apart. Next he examined those that had scabs; and he took and hewed many of these, and commanded the virgins to take them up and cast them into the building. And the virgins lifted them up, and put them in the middle of the building of the tower. And the rest he ordered to be laid down beside the black ones; for these, too, were found to be black.
He next examined those that had cracks; and he hewed many of these, and commanded them to be carried by the virgins to the building: and they were placed on the outside, because they were found to be sounder than the others; but the rest, on account of the multitude of the cracks, could not be hewn, and for this reason, therefore, they were rejected from the building of the tower. He next examined the chipped stones, and many among these were found to be black, and some to have great cracks.
And these also he commanded to be laid down along with those which had been rejected. But the remainder, after being cleaned and hewn, he commanded to be placed in the building. And the virgins took them up, and fitted them into the middle of the building of the tower, for they were somewhat weak. He next examined those that were half white and half black, and many of them were found to be black. And he commanded these also to be taken away along with those which had been rejected.
And the rest were all taken away by the virgins; for, being white, they were fitted by the virgins themselves into the building. And they were placed upon the outside, because they were found to be sound, so as to be able to support those which were placed in the middle, for no part of them at all was chipped. He next examined those that were rough and hard; and a few of them were rejected because they could not be hewn, as they were found exceedingly hard. But the rest of them were hewn, and carried by the virgins, and fitted into the middle of the building of the tower; for they were somewhat weak.
He next examined those that had stains; and of these a very few were black, and were thrown aside with the others; but the greater part were found to be bright, and these were fitted by the virgins into the building, but on account of their strength were placed on the outside.
Source: The Pastor (or "The Shepherd") (New Advent)