Noun : the hardpan of mathematical theory.    From Dictionary.com. 

Caliche is also known as hardpan, calcrete, kankar (in India), or duricrust.    From Wordnik.com.  [WN.com - Business News] Reference

Caliche is also known as hardpan, calcrete, kankar (in.    From Wordnik.com.  [WN.com - Business News] Reference

The hardpan had disintegrated in places to mere rubble.    From Wordnik.com.  [The Gunslinger]

Its bulbous jelly tires crunched on the Dry Basin's hardpan.    From Wordnik.com.  [Asimov's Science Fiction]

This high land is heavy clay underlaid with considerable hardpan.    From Wordnik.com.  [Northern Nut Growers Association, report of the proceedings at the sixth annual meeting Rochester, New York, September 1 and 2, 1915] Reference

Even the best inheritance cannot prevail against hardpan or worn-out soil.    From Wordnik.com.  [Northern Nut Growers Association Report of the Proceedings at the Thirty-Seventh Annual Report Wooster, Ohio, September 3, 4, 5, 1946] Reference

Muscled, tanned men who didn't mind digging a hole in this alkali hardpan.    From Wordnik.com.  [grouse Diary Entry] Reference

You took the devil's coin and killed a better man out there on the hardpan.    From Wordnik.com.  [Alfred Hitchcock's Mystery Magazine]

Despite the rain earlier the hardpan was dry just inches beneath the surface.    From Wordnik.com.  [She Is The Darkness]

Soon there was nothing more than a pair of deep ruts worn through the hardpan.    From Wordnik.com.  [Echo Burning]

Jake was halfway across the stable yard, cowering on the cracked, rubbly hardpan.    From Wordnik.com.  [The Gunslinger]

The beds were dug down below the hardpan and the dirt sifted to remove the rocks and caliche.    From Wordnik.com.  [Simple Winter Hoop Garden Part 1] Reference

The presence of clays, hardpan or coarse gravel beds may slow down or impede drilling to continue.    From Wordnik.com.  [6. Water sources, their protection and development] Reference

Determine the physical nature of the bedding, e.g. if a deposit is calcrete, is it a hardpan type.    From Wordnik.com.  [4. Testing and Quality Control] Reference

Subsoils contain a layer enriched with lime and/or gypsum, which may develop into a caliche hardpan.    From Wordnik.com.  [Intermountain Semidesert Province (Bailey)] Reference

In the lower bajada (bottom land) the soil is sandy and fine-textured, often with "caliche hardpan.".    From Wordnik.com.  [Desert biome] Reference

Away across the desert's hardpan horizon the waves of heat rippled, taunting me with a mirage of hope.    From Wordnik.com.  [William] Reference

Water was absorbed slowly, very slowly, by the arid hardpan and tended to trickle toward any depression.    From Wordnik.com.  [Fierce Invalids Home From Hot Climates]

He had hit that scourge of every local farmer -- hardpan, an impervious, cement-like mass of clay and silt.    From Wordnik.com.  [A Garden Grows Underground] Reference

Inceptisols, a classification of newer soil formation, occur where the soil removal process has reached hardpan.    From Wordnik.com.  [1. Labour productivity and distribution] Reference

They pounded across the hardpan, scurried into the protection offered by the surrounding boulders, and set up shop.    From Wordnik.com.  [The Flood]

The subsoil is always very poor; it contains no mineral salts; it does not become hard and does not form a hardpan.    From Wordnik.com.  [Chapter 5] Reference

The predominant natural plant communities are Needlegrass grasslands, and Northern hardpan vernal pools are common.    From Wordnik.com.  [Hardpan Terraces] Reference

No. 12, 447 yards, par 4: A waste area of hardpan sand and wire grass stretches down the right side of the fairway.    From Wordnik.com.  [U.S. Open hole descriptions] Reference

The land was flat, dry, and featureless, mostly hardpan cut through here and there with a swath of coarse sandy soil.    From Wordnik.com.  [The Pillars of Creation]

It performs better than most trees where soils are sterile, stony, and shallow, or where there is a hardpan near the surface.    From Wordnik.com.  [3 The Tree] Reference

They were on a secondary road, graded hardpan, angling west by southwest, into country that opened up like a door into outer space.    From Wordnik.com.  [Alfred Hitchcock's Mystery Magazine]

Two small freshwater wetlands have two small ponds that may be pocketed on bedrock or be underlain by tight soil material (hardpan).    From Wordnik.com.  [Narragansett Bay National Estuarine Research Reserve, Rhode Island] Reference

The dredges made great headway at first, as long as there was only surface mud to contend with, but then they hit hardpan and boulders.    From Wordnik.com.  [The Great Bridge] Reference

Acacia tumida has great potential for stabilizing moving sands, while A. cowleana and A. colei can tolerate hardpan near the soil surface.    From Wordnik.com.  [Chapter 48] Reference

The soils of the Rufiji basin are friable, acidic and nutrient-poor, unsuited to agriculture and in the south, alkaline sands over hardpan.    From Wordnik.com.  [Selous Game Reserve, Tanzania] Reference

The soil was light sand with a clay hardpan three feet down.    From Wordnik.com.  [Three Acres and Liberty] Reference

His lie looked like one of those sandy/hardpan lies you get on a lot of munis.    From Wordnik.com.  [SI.com] Reference