One of the most vivid of the mythical episodes added to the history of the Celtic captain, Arthur, is that deed by which he was disclosed to be the predestined king. His father, Uther Pendragon, had died, and the powerful lords of the kingdom were all grasping for the crown. By Merlin' s advice and counsel it was finally decided that the supernatural powers should be left to determine the troubled issue. Before the greatest church in London a stone had appeared in which a sword was buried and letters of gold were to be seen on the stone around the sword to the effect that the one who could draw the blade should be recognized as king. Many tried in vain. Then, at last, this unknown youth, Arthur, who had been reared secretly under that guardianship of Merlin, rode up to the church and, ignorant of the magic of his deed, pulled out the sword. This striking symbol of the hero' s election and sacred power is derived from the prehistoric period at the close of the Age of Stone. Swords were not made until after the discovery of bronze and iron: before that time there were only spears and arrows and axes. And so, who is the one who frees the metal from the stone? The culture hero: the magic smith, who released the worlds from the Stone Age and taught mankind the art of smelting bronze and iron from the ore. The hero who cart draw the iron sword from the stone is not necessarily a great warrior, but always a powerful magician, a lord over spiritual and material things: a seer comparable, in terms of the Iron Age, to modern inventor, chemist or engineer, who creates new weapons for his people. And just as today we live in awe and some fear of the man of science so it is only natural that the folk of that faraway other day should have thought of the one who freed for them metal from stone as the chosen master of the secrets of existence. In the third sentence of paragraph, the 'troubled issue' refers to______.