Hydrogeology terminology An earth formation that is porous and can absorb water but does not yield an appreciable supply to wells is termed:

Introduction / Context:
Correct classification of subsurface formations is essential for groundwater exploration and well design. Terms differentiate formations by porosity and permeability.

Given Data / Assumptions:

• Formation is porous (stores water).
• Formation does not yield appreciable water to wells (very low permeability).

Concept / Approach:
An aquifer is both porous and sufficiently permeable to yield water. An aquiclude is porous but effectively impermeable, thus it stores water but does not transmit it in useful quantities. An aquifuge is neither porous nor permeable. An aquitard is semipermeable and yields water slowly.

Step-by-Step Solution:

Verification / Alternative check:
Clay formations often function as aquicludes; coarse sand or gravel is typical of aquifers.

Why Other Options Are Wrong:

• Aquifer (a) yields appreciable water.
• Aquifuge (c) is nonporous and impermeable.
• Aquitard (d) does yield some water, albeit slowly.

Common Pitfalls:
Confusing aquiclude with aquifuge; porosity is the key differentiator.

Final Answer:
Aquiclude