The formation of new ocean crust occurs at volcanic 'mid-ocean ridges.'

新的海洋地壳的形成发生在火山的“海洋中脊”。

He set out across country, cutting through the gaps in the volcanic ridges and crossing the flat or rolling country between.

他出发穿越乡村， 穿过火山山脊的缝隙， 穿过其间平坦或起伏的乡村。