Screen-washing bulk samples of fossilliferous matrix is the method of choice for concentrating relatively large numbers of small fossils from unconsolidated sediments. The technique is most effective when used to disaggregate dry and unconsolidated sand, silt, and silty clay. Ideally, when the dry fossil-bearing particles will pass through an appropriate size screen-mesh, leaving behind a residue of fossils and coarser grain sizes. Organic-rich sediments, overconsolidated silt, silty clay, maris and clays may require soaking in dilute chemical solutions to encourage disaggregation. The extraction of fossils from these more intractable sediments, therefore, generally will be limited to the processing of quantitatively small samples (several hundred grams), in the laboratory.