If you find an old log that is well rotted, break it open and look for roots growing UP into this source of nutrients. These roots that defy both gravity and the normal laws of root behaviour are important where the source of nutrients is above the soil rather than deeper down in the soil. Note how leaves in the litter are sequenced from newest to oldest. Look for examples of leaves of the same species and see the stages of decay. Dig down into the soil under the leaf litter layer.
Organic matter gives soil a darker colour.
Organic matter means plant nutrients. Note where the roots are. The roots are concentrated in the surface layer where all the action takes place. The litter is added to the top and the litter organisms convert it into soluble minerals that the roots can absorb. Some rainforests away from the beach are to be found growing on what appear to be piles of rocks.