hard stratum

例句：

1. 1. The rock is composed of a hard stratum of minerals.
   这岩石由一层坚硬的矿物组成。
2. 2. The soil is very hard stratum, which makes it difficult for plants to grow.
   土壤非常坚硬，使得植物难以生长。
3. 3. The hard stratum can be easily broken by the impact of heavy rain.
   坚硬的地层很容易被大雨的冲击而破碎。