(1) A hard layer of rock covered by soil, sediment, etc. , and more or less continuous over a large region. It is distinguished from silt, clay, etc. , by being hard, and from sand, pebbles, and boulders by being continuous. Bedrock which has been cleared of its covering is referred to as exposed bedrock. Large, deeply imbedded boulders, with upper surfaces planed and leveled through exposure, are some-times erroneously reported as bedrock in descriptive writing. (2) A stratum of rock in the Earth's crust which has been formed in an approximately horizontal position.