“砂砾层”用英语怎么说？

沙砾覆于铁质土层与砂砾层之上.Gravelly - sand over an iron - pan and gravel layer.小石头、砂砾层也可用来做隔绝层,以保持水分,降低土壤的温度.Pebbles and gravel also insulate the soil to keep surface temperatures low and preserve water.古河谷的边缘地带,往往缺失底部的河床相砂砾层.The ed...