They can date layers by the fossils that are found in them.If a layer has a fossil in it that is known to be 50 million years old the layer itself must be at least 50 million years old and the layers below it have to be older than 50 million years.of new mineral grains that are larger than the original grains.As the sediments recrystallize they arrange themselves in a series of interlocking crystals that connect the other grains together into a solid rock.Weathering is the process of breaking down rocks and minerals into smaller pieces by water, wind, and ice. Streams and rivers carry sediments in their current.When the current slows around a bend or the river empties into a lake, or ocean, or another river the sediments fall out because of gravity.Shale, sandstone, and limestone are the most common types of sedimentary rocks.
Natural agents of deposition are water, ice, gravity, and wind.
The larger sediments fall out first and the lightest sediments fall out last.
The diagram above shows layers of sediment that were laid down in a lake.
In the spring the lake receives an influx of water from the mountain snow melt.
This snow melt carries with it a large amount of sediment that becomes suspended in the lake water.