煤形成地质过程：数百万年，湖泊干涸，植物被埋入地下，经过长时间的埋藏作用，这些植物逐渐转化为煤炭---**Chart/Diagram Description:** * **Type:** This is a three-dimensional block diagram or geological cross-section illustrating a natural landscape with a river and underlying soil layers. * **Main Elements:** * **River:** A winding river flows from the background towards the foreground, occupying the central part of the surface. Its water appears light blue. A brown log is floating in the river. * **Land Surface:** Green grassy areas form the banks of the river. Several palm trees with brown trunks and green fronds are sparsely distributed on these banks, predominantly on the right side and in the background. * **Underground Layers (from top to bottom visible):** * **Topsoil/Soil:** Directly beneath the green grass is a reddish-brown layer, indicating topsoil or a superficial soil layer. * **Peat Layer:** Below the reddish-brown layer is a darker brown to blackish layer, explicitly labeled as "泥炭" (Peat). This layer appears to be thicker on the right side of the cross-section and thins out towards the left. Part of this layer is shown to be beneath the riverbed. * **Subsurface Layer:** Beneath the peat layer, a much thicker, yellowish-brown granular layer is depicted, representing deeper geological material (e.g., sand, gravel, or bedrock). * **Labels and Annotations:** * **泥炭 (Peat):** This label points with a line to the dark brown/blackish layer beneath the reddish-brown soil. * **a:** The letter "a" is enclosed in a light gray circle, positioned in the lower-left foreground of the diagram, not pointing to any specific object but serving as a general identifier for this part of a potentially larger series. * **Arrow:** A horizontal green arrow points to the right, located in the upper-right section of the image, above the land surface, suggesting a direction (e.g., of flow, time, or a process).