"There is a treaty between Norway and Sweden, more than one hundred and fifty years old, which provides that Swedish Lapps can go to the coast of Norway in summer, and Norwegian Lapps can go inland to Sweden in winter," Lieutenant Ekman told the children. "Yes," said Erik, "when the moss is scanty or the swarms of mosquitoes too thick, the reindeer hurry off to some pleasanter spot, without stopping to ask permission. Perhaps we have been in camp a week, perhaps a month, just as it happens; but when we hear their joints snapping and their hoofs tramping all together, we know it is time to take down the tent, pack up everything and follow the herd to a new pasture." "I am glad we are out of sight of the photograph shops in Gellivare, anyway," Birger told Erik, when they were seated in the light carts and were once more on their journey. "If I could take such good pictures myself, I shouldn't care; but all my pictures of the midnight sun make it look like the moon in a snow-bank." Just then Gerda, who was riding with her father, called to Birger, "Stop a moment and listen!" So the two posting-carts halted while the children listened to the music of a mountain stream not far away. Mingled with the sound of the rushing water was the whirr of a busy sawmill in the depths of the woods, while from the tree-tops could be heard the call of a cuckoo and the harsh cry of a woodpecker. Soon they were on their way again, pushing deeper and deeper through the Lapland forest; their road bordered with green ferns and bright blossoming flowers, their path crossed now and again by fluttering butterflies. "This is just the right kind of a carriage for such a road, isn't it?" said Gerda, as the track led through a shallow brooklet. "Yes," answered her father; "a few of the roads in these northern forests are excellent; but many of them are only trails, and are rough and rocky. If the cart were not so light, with only one seat and two wheels, we should often get a severe shaking-up." "How does it happen that we can get such a good horse and cart up here among the forests?" asked Gerda. "As there is no railroad in this part of Lapland, the Swedish government very thoughtfully arranges for the posting-stations, and guarantees the pay of the keepers for providing travellers with fresh horses," her father explained. "The stations are from one to two Swedish miles apart, and everyone who hires a horse is expected to take good care of him." "I'm afraid we shall have to make this horse go faster, or we shall be caught in a thunder-storm," said Gerda, looking up through the trees at the sky, which was growing dark with clouds. "You are right," answered her father; and at the same moment Erik looked back and shouted, "We must hurry. Perhaps we can reach my father's tent before the rain comes." Then, glancing up again at the black clouds, he said to Birger, "We shall soon hear the pounding of Thor's hammer."