Siliceous frustules of diatoms being indestructible, piled up at the bottom of ocean and formed a thick bed over billions of years. Such a thick bed is known as

Answer: BSolution: The diatom shells piling up at the bottom of oceans over milions of years formed deposits called diatomaceous earth. These deposists may be thousand meters thick with as malny as five million diatom shells in each cubic centimetre. This diatomaceous earth is used in many small and large scale industries.