The legend is that Newton discovered Gravity when he saw a falling apple while thinking about the forces of nature. Whatever really happened, Newton realized that some force must be acting on falling objects like apples because otherwise they would not start moving from rest.
I would say that in very fast moving water such as in a river, the cobble size could be transported because cobbles are 64-256mm so are quite big and in a quiescent stream won't move much but in a freshet say in a steep mountain stream they can be rolled along such as I observed in the local streams at a mining town during the Hurricane Fifi in Honduras in 1974.
These primitive plants can be found in any mouse humid environment. More specifically a forest because the like to be under the tree canopy with low light. An example of a forest you would find these in is the Olympic national forest in Washington (the pacific coast)
The index fossils are fossils that are found in the rock strata of certain geologic period, but they are also fossils that are very common and can be found in numerous places around the globe.
Because they can be found all over the globe, and they are indicative of certain geologic period, the geologists have started to use them as a simple way of determining the age of the rock strata. While this method can not provide the geologists with an accurate year for the formation of the rocks, it is still able to determine the relative age of the rocks. By determining the relative age with such ease by using the index fossils, the geologists are able to immediately make conclusions about the rock strata, have basic information about it, and largely be aware of the processes that formed them and influenced them.
