Professor Leidy, of Philadelphia, has detected about thirty remains of species of extinct mammalia. Many of these belonged to animals such as the hippopotamus, rhinoceros, tapir, etc. One extinct animal, called the Oreodon, had grinding teeth like lions, cats, etc., and must have belonged to a race that lived on vegetables and flesh, and yet chewed the cud like a cow. Another called the Machairodus, was wholly carnivorous, and combined the size and weight of the grizzly bear with the jaws and teeth of the Bengal tiger. Most of the bones are yet in good preservation and highly mineralized. Dr. Owen says he saw all the bones of a skeleton eighteen feet long and nine in height; also a jaw of a similar animal, which measured five feet along the range of its teeth. At one place there is a valley which has the appearance of a floor of an ancient lake, where turtles lie imbedded by hundreds, and some weighing a ton. This wonderful place looks like the city of the dead; and as nothing grows there, and there is no water for animals, no living thing is found there, not even a bird. General Sully made a forced march through it with cavalry a few years ago, and had to carry water for the men and horses. The Indians never go there, unless driven in by some tribe attacking in superior numbers. The fossils which have been brought from the Mauvaises Terres belong to a species that became extinct before the period when the Mastodon inhabited this country. The strata in which these animals are imbedded indicate that the water was fresh or brackish. It is the most desolate and barren prospect one could lay his eyes on; and if the place for bad people is like this, when they come to die, may no boy have to go there and be frightened all his life-long for his wicked and cruel deeds to others, or to animals either; for the sight of these skeletons is enough to make any boy afraid of disobeying his mother, or to go to sleep any night without being sorry for his sins. Gold is said to be deposited there, and may yet be found in large quantities, if the Indians can be induced to let the whites prospect there. A while since, an Indian brought into a fort some gold-dust and a large nugget. The post-trader looked at it and pretended it was iron, saying to the Indian, "No good." He threw it out of the window and gave the Indian a glass of whisky. When he went out, the trader picked it up, and it was worth thirty dollars. The Indian having refused to tell where he got it, was made quite drunk, and then he said it came from the Bad Lands; but if the chief found out he had told of it, he would kill him. NATURAL HISTORY--ANIMALS ON THE PLAINS. The animals which are found west of the Missouri River, especially in the Rocky Mountains, and far beyond them, are the buffalo, elk, deer, cimarron bear, mountain sheep, antelope, coyote, prairie-dog, etc.