As Nicky did not put in an appearance that night, they set out next morning northward, leaving Baderoon to skin out birds in camp. The curator did not worry over Nicky. In his rucksack the lad had carried his odd nightgear, of an old bathing suit with the armholes sewed up to pull over his bed, a pair of extra socks to cover his arms and another for his feet. So dressing up to go to bed, Nicky would turn in on a leaf patch, secure from insects and snakes, and, with Sadok to guide him, would be abundantly able to care for himself. After several hours’ travel to the north the going became more rocky and the vegetation sparse and thorny. Soon open skyline appeared ahead, and then they came upon the rocky cliffs of basic limestone that border the south bank of the river Majkor, which separates the Aru mainlands of Maykor and Kobror. The north bank was high jungle, and up and down its reaches it was a true river, a deep, narrow channel winding through the jungle as far as the eye could reach. Yet its waters were salt. “That’s really wonderful, sir!” cried Dwight, enthusiastically, when he had grasped the full significance of it. “Lots of small islands like England, for instance, have rivers; but they are true rivers, rising in the mountains somewhere. Others have salt straits dividing them from the mainland, like Staten Island, at home. This channel can’t be a fissure, for it winds and turns just like a river. What is Wallace’s theory, Mr. Baldwin?” he asked, giving it up. “The true one, I think,” replied the curator. “The west coast of Aru is deep water; the east, a shallow pearl sea, clear over to New Guinea. That sea was undoubtedly formed by gradual subsidence of the sea bottom. It is only three hundred feet deep; so that would not take long for geology to accomplish. The coast of New Jersey is rising two feet a century. At no very distant date, then, New Guinea and Aru were one big continent, with all the sea between lowlands--very like those that extend now back from the coast to the Great Precipice over where we are soon going. The rivers, then, like the Outanata and the Mimika, must have flowed through those lowlands, and these channels of Aru were part of them, emptying into the sea on the west coast of Aru. Can’t you see how important this little trip of ours is, now? This river can tell us something of the mineralogy of the unexplored interior of New Guinea! And without our ever going there, for that matter!” “Sure it can--if we had a long line and a grappling hook to dredge with!” said Dwight, practically. “We have the former!” smiled the curator, producing out of his rucksack a hank of strong green Banks line, “and we’ll make a grappling.” Near by grew a tree of the Erythina family, its profuse scarlet blossoms a grand note of color against the gray cliffs. Thousands of swallows swooped about the latter, and the curator eyed them absorbedly.