The rocks in the Arakan range and its spurs are metamorphic, and comprise clay, slates, ironstone and indurated sandstone; towards the S., ironstone, trap and rocks of basaltic character are common; veins of steatite and white fibrous quartz are also found.
Next in antiquity to hydraulic lime is Roman cement, prepared by heating an indurated marl occurring naturally in nodules.
They are rarely metamorphosed to the point of recrystallization, though locally shales are altered to roofing slates, sandstones are indurated, limestones slightly marblized, and coals, originally bituminous, are changed to anthracite in northern Pennsylvania, and to graphite in Rhode Island.
As in all such cases, the plain consists of marine (with some estuarine and flu viatile) stratified deposits, more or less indurated, which were laid down when the land stood lower and the sea had its shore line farther inland than to-day.
Normally the pleon carries six pairs of two-branched appendages, of which the first three are much articulated flexible swimming feet, the last three few-jointed comparatively indurated uropods.
The Dakota formation is largely sandstone, which gives rise to hogbacks where it has been tilted, indurated and exposed to erosion along the eastern base of the Rocky Mountains.
The common description of " the Oriental " as indurated in his antagonism to the alien conqueror here perhaps has some truth in it.
In 1779 three beds of rock-salt were discovered at Lawton, separated from one another by layers of indurated clay.
It was worked for about a hundred years in only its upper bed, but in 1781, after traversing a layer of indurated clay intersected with small veins of salt 102 yds.
In some regions, notably in the Baltic province and in parts of the United States, the rocks still retain their original horizontality of deposition, the muds are scarcely indurated and the sands are still incoherent; but in most parts of the world they bear abundant evidence of the many movements and stresses to which they have been exposed through so enormous a period of time.