圆砾岩

例句：

1. 1. The riverbed iscovered in a layer of smooth, roundgravel.
   河床覆盖着一层光滑的圆砾。
2. 2. The beach was littered withrounded pebbles and shells.
   海滩上满是圆润的鹅卵石和贝壳。
3. 3. The engineer used round gravel to reinforcethe foundation of the bridge.
   工程师用圆砾加固了桥梁的基础。