先: 名词1.(时间或次序在前的) earlier; before; first; in advance 短语和例子有言在先 make clear beforehand; 争先恐后 strive to be the first and fear to lag behind; 你不必先付款。 you don't have to pay in advance. 你先拟个提纲再写。 m
Planation surface is a wide - ranging and undulating surface formed by planation in a long and relative stable period or in a decreacing - development period . it is near the base level and there always exists some deposits such as crust of weathering above it . planation surface is often uplifted or buried by the later tectonic activities 夷平面是在长期的地壳相对稳定时期或地壳下降发展阶段，由广泛的夷平作用以截断面形式横切所有先成的地层和构造的接近侵蚀基准面的平缓的地表形态，其上常有风化壳等碎屑堆积，常遭到后期的抬升切割或埋藏，分布于地球的各纬度带。
