calcareous concretions

例句：

1. 1. The fossilized shells of the ancient sea creatures are a fascinating study of how life evolved over time.
   古代海洋生物的化石是研究生命如何随时间演变的迷人课题。
2. 2. The sedimentary rocks containing these calcareous concretions are often used as building materials in construction.
   含有这些钙质硬壳沉积物的沉积岩常被用作建筑用材料。
3. 3. The ocean floor is littered with these calcareous concretions, which have formed from the calcium carbonate deposited by marine organisms.
   海洋底部遍布着这些钙质硬壳沉积物，它们是海洋生物沉积的碳酸钙形成的。