THE GIANT PAINT POT IT was indeed a sight well calculated to make the boys stare, and rub their eyes in wonder, as though they half believed they must be dreaming. If these wonders of Yellowstone Park elicit cries of delight from tens of thousands of tourists in these modern times, imagine how remarkable they must have seemed to these pioneer lads more than a hundred years ago. "When you called it a paint pot, Roger, I think you hit the bull's-eye, for it does look like that, with all those colors boiling up in such a crazy fashion!" Dick presently remarked, breaking the spell that seemed to bind them. "But what is it made of, I'd like to know?" demanded the puzzled Roger. "Colored clay, in the shape of mud, that is boiling all the time. Be careful how you put your hand to it. See how the steam keeps on rising. It must be pretty hot stuff!" "But what makes it boil that way? There must be a fire of some kind deep down in the earth?" "Nothing else would make all these fountains of hot water, and even the rocks in some places feel warm," admitted the other lad, who was hardly less amazed than Roger himself. "It must be some sort of volcano," Roger continued, thoughtfully. "It has no visible cone, like most of them do, and so the heat escapes in this way through hundreds of little vents." That is about the nearest explanation any scientist has ever been able to give why this one region in all the world contains innumerable geysers, hot springs, boiling colored mud pots, and various other wonders of Nature. (Note 5.) "All I can say is that I don't blame any poor Injun for believing the place is Evil Ground," muttered Mayhew, as he stared at the strange spectacle of that blue and yellow and green mud boiling ceaselessly, and throwing off steam that had a peculiar odor, unlike anything they had ever smelled before. He looked around him, and shrugged his shoulders. So many remarkable things were to be seen, such as a frontiersman might well view with alarm, that it was no wonder Mayhew felt uneasy. Left to his own devices he would have turned his back on this enchanted region, and considered himself a lucky man if only he might get away with his life. "It strikes me," Dick observed, "that we need not hope to find Williams anywhere about here, if, as we fear, he has been taken prisoner by those Blackfoot Indians." "No, because they would never come to a place like this, unless their old medicine man was along to make a palaver with the Evil Spirit," Roger suggested. "That is what I heard a Mandan brave say, and I guess it must be about so. We will have to go further, and look for Jasper elsewhere." Mayhew seized upon this hint to make a start, and, noticing how anxious the scout seemed to be to shut out the strange spectacle of that ever boiling pool of gayly tinted mud, the boys followed at his heels.