coal seam

例句：

1. 1. The coal mine is located in the mountainous region.
   煤矿位于山区。
2. 2.The coal seam is mined for its valuable minerals.
   煤层被开采以提取其有价值的矿物。
3. 3. Coal seams are formed by the accumulation of organic matter over millions of years.
   煤层是由数百万年有机物质的积累形成的。