What does strata mean here? What does strata mean here ?


  These consolidated layered strata are known as stratified rocks. The
  strata vary in thickness and may be tilted or horizontal. The
  sediments consist of loose particles of gravel, sand, silt in various
  proportions hence are porous and permeable.


It comes from a chapter called Materials of The Earth Crust-Rocks from Frank Morden's Geography Class IX Part 1
Strata always mean a collection of layers. A single layer is called a stratum. The plural of stratum is strata.