"No, my dear little girl, trees don't grow in straight lines anywhere," said the Doctor, laughing--"except when they are planted so. The 'timber-line' of a mountain is the edge of the woods, above which no trees grow, and we see nothing but bare rocks, and the few low plants that cling to the cracks among them. Well, we had hardly rested long enough to get our breath after such a climb, when we heard a rich ringing song, something like a House Wren's, but louder and stronger, and very quick, as if the bird were in a great hurry to get through. But he wasn't, for he kept saying the same thing over and over again. Presently we spied him, on the tiptop of a pile of stones, standing quite still, with his head thrown back and his bill pointing straight up. He looked gray, dusted over with pepper-and-salt dots on the back, and his bill was very straight and sharp--almost an inch long, it looked. This was a Rock Wren." "He must have had a nest somewhere in those rocks," said Rap. "Wrens most always have nests near where they sing." "No doubt he had, as it was the nesting season--June," answered the Doctor; "but it was growing late in the day, we had a long scramble down the mountain before us, and could not wait to hunt for it. Most likely, too, if we had found the very place where it was, we should not have been able to see it, for probably it was tucked away too far in a crooked passage under a shelving rock. "When we were half-way down the mountain we passed a miner's cabin. He was at home, and we sat down on a bench by the door to rest. Thinking he might know about the nest of the Rock Wren,--for an old miner knows a great many things he never thinks of making a book about,--I asked him if there were any Wrens around there. "'Wall, I should smile, stranger! Lots on 'em--more'n one kind, too--but mostly not the reg'lar kind they have where you tenderfoots live--bigger, and pickeder in front, and make more fuss. When they fust come, 'long about May, or nigh onter June, they act kinder shy like, but they get uster to yer, soon's they find nobody ain't goin' to bother with 'em, and stay around altogether, mostly in the rocks. Last y'ar there was two on 'em come nigh chinking up this shebang with trash they hauled in for a nest, afore they got it fixed to suit 'em, and had it chuck full o' speckled eggs. Then one of these yere blamed pack-rats tore it all up, and they had to start in to hauling more trash.' "So you see, children, this miner knew a Rock Wren--do you know a Jenny Wren?" The Rock Wren Length nearly six inches. Back gray, with fine black-and-white dots. Under parts no particular color. Some of the tail-feathers with black bars and cinnamon-brown tips. A Citizen of the United States from the Rocky Mountains to the Pacific Ocean. A Ground Gleaner THE HOUSE WREN "We all know Jenny Wren!" cried the children. "The Farm is full of Jennies and Johnnies!" "They build in bird-boxes," said Dodo.