雅思阅读材料：Amazon River

　　"Wobble board" effects

　　While demonstrated most spectacularly in the Amazon Basin, continental tilting is known to have occurred elsewhere, including in our own backyard.

　　"The idea of sinking slabs is shown to have occurred in North America and there are applications to Australia," says Grace, where eastern parts of the country are believed to "have swung up and down like a giant wobble board." Grace says it is possible that similar tilting has created and destroyed other large river systems over time, such as a Triassic-era (from 200 to 250 million years ago) movement perhaps responsible for forming Sydney’s bedrock, the Hawkesbury sandstone.

　　Geophysicist Louis Moresi from Melbourne’s Monash University, who was not involved in the research, says the team’s work is fascinating and demonstrates the way in which continental tilting can influence river systems over millions of years.

　　"An additional 400 m of topography might not seem much in contrast with the height of the Andes, but it is a very broad-scale tilting of the continent which drainage and erosion cannot resist," says Louis.