我们所看到的石灰岩层高达一千米，而宽却只有几米，沿着沙漠底部和沙丘间的山谷分布。
They're up to a kilometer long, but only a few meters wide, and they're scattered along the desert floor, in valleys between the dunes.
撒哈拉沙漠是一个沙质沙漠，有很多沙丘。
该国的主要地形是沙漠平原和沙丘，还有环绕尼日尔河的一个大草原。
Currently most of its terrain is made up of desert plains and sand dunes with some savanna around the Niger river.
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