层理是指岩层中物质的成分、颗粒大小、形状和颜色在垂直方向发生改变时产生的纹理，常见于大多数沉积岩和一些火山岩中，是研究地质构造变形及其历史的重要参考面。沉积岩中层理的形成可能是沉积物结构和成分的变化或者沉积间歇、沉积季节的变化所致。火山碎屑物在其爆发和降落过程中，由于重力、颗粒大小和风的影响，成岩时会形成具有分选性的层理。

Bedding refers to the textures caused by the changes of composition, size, shape, color in vertical direction. Those textures usually can be seen in most sedimentary rocks and some magmatic rocks, which plays an essential role in studying geological structure deformation and its development. The stratification formed in sedimentary rocks could be due to the changes in sediment structure and composition or sedimentary intermittent and seasonal alternation. During the diagenetic process, influenced by gravity, particle size and wind, bedding of sorted behaviour was formed.