These clastics are derived from an outside source and incorporated into the soil parent material. Identification depends on recognition of structure and individual components, and consideration of possible sources. Shales and siltstones frequently show bedding and limestone may have fossils. The presence of lithorelicts often gives clues to the origin of the soil such as glacial outwash. Artifacts are items that may be observed in thin section but have been introduced during sample preparation.
Foreign objects introduced in the section include lint fibers , grinding compound , and bubbles .
Other artifacts may include grain fracturing, shrinkage cracks caused by sample desiccation or resin shrinkage, void areas due to grain plucking or imcomplete impregnation, improper or uneven polishing, and slight birefringence of the impregnating medium caused by strain or improper curing. Orgainic Matter . Most soils support both plant and animal life, both of which may reach considerable depths and leave evidence of their passage. Organic matter may occur in shades of brown or black and may show evidence of cellular structure. Near the surface, organic litter and decomposed products may be common.