Complex sentence: In some parts it rises into irregular uplands and elevated plains, interspersed with detached rocks; in others it sinks into marshy lowlands, which frequently remain under water during the rainy season.
Split into simpler sentences: In some parts, it rises into irregular uplands and elevated plains, interspersed with detached rocks. In others, it sinks into marshy lowlands, which frequently remain under water during the rainy season.