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密苏里河流经美国蒙大拿州东部,横穿过一组被称为海尔克里克的原始岩层。这是在约6500万年前的晚白垩纪,由沙岩、粉砂岩和泥岩形成的一组厚厚的岩层。当时,这个区域是河道纵横的低凹泛滥平原,旁边就是一道如今已消失的海岸线。许多种类的恐龙和其他动物在此繁衍生息。海尔克里克岩层富含恐龙化石,是世界上最大的一个恐龙墓地。也正是在此,人们于1902年挖掘出了第一块暴龙化石和其他一批著名的化石标本。
The Missouri River runs through eastern Montana, the United States, across a group of primitive rock formations known as the Haarleigh. This is a group of thick rock formations formed from sandstone, siltstone and mudstone about 65 million years ago in the late Cretaceous. At the time, the area was a low-lying floodplain of waterways, next to a now-disappearing coastline. Many species of dinosaurs and other animals multiply here. The Haier Crick rock formation is rich in dinosaur fossils and is the largest dinosaur graveyard in the world. It is also here, in 1902, people unearthed the first tyrannosaur fossils and a number of other famous fossil specimens.