During all this conversation Jackson and Jimmie had kept steadily at work sewing the new, strong canvas taken from the tent on the frame of the planes.  They could not make a very neat job of it, but they did their work well.  Ned had hope of getting out of the valley that very night.  Presently the men on the ledge withdrew for a time, and Ned began a closer examination of the Nelson.  To his disgust he discovered that the gasoline was very low in the great tanks.  Built for long flights, the Nelson's tanks were very large, fitted to carry a supply which would last a couple of days.  Ned did not quite understand why the supply should be short after a run of only three or four hundred miles.