The sediment comes from eroded rocks carried there by rivers or ice, and from the skeletons of ... causing them to change into another type of rock. They are usually resistant to weathering ...

As it cools it becomes a very hard type of igneous rock. This one first formed over 350 million years ago. Then, millions of years after that, during the last ice age - when the land was covered ...

For example, acid rain dissolves limestone to form karst, a type of terrain filled ... Back up on the mountains, snow and ice build up into glaciers that weigh on the rocks beneath and slowly ...

The investigation began with a geological mystery: the presence of rocks that, by their nature, do not match the types of formations currently present ... creating a chaotic mix that becomes trapped ...