§ 6, 7. 



VEINS AND VAULTS. 199 



direction, as the series a, b, c, d, on the beds 1, 2, 3, 4, — 

 as if a set of horizontal volumes were placed flat on the 

 inclined edges of another series of books, — they are termed 

 unconformable. 



6. Veins and faults. — But the strata have not only 

 suffered change of position, they have also been rent and 

 broken, and are traversed by cracks or fissures, which in 

 some instances are filled with bones, pebbles, and stalacti- 

 tical concretions (p. 78), and in others with mineral mat- 

 ter, and veins of metalliferous ores. The term fault is 

 applied to those fractures and displacements which are 

 accompanied with the subsidence of one part of a mass, and 

 the elevation of another. This is exemplified in the section 

 of the carboniferous strata represented in Lign. 32, in 

 which the layers, or seams of coal (1, 2, 3, 4), have been 

 shifted to a higher level on the left hand, though both 

 sides of the rock remain in apposition ; f, marks the line 

 of fault. Strata, in fact, may be compared with the layers 

 of masonry in a building ; beds of clay representing the 

 mortar, and those of harder rocks the courses of brick 

 or stone ; while the fissures, veins, and faults, are analogous 

 to the cracks, sinkings, and displacements, produced by 

 the settling of different portions of the edifice after its 

 erection. 



7. Chronological arrangement of the strata. — In 

 the alluvial beds of gravel, sand, and marl, containing the 

 remains of the large herbivorous mammalia, which formed 

 the principal subject of the previous discourse, but few 

 indications of regular stratification are observable ; the 

 deposits for the most part consisting of materials that have 

 been transported by rivers or currents, or drifted by ice- 

 bergs, and accumulated in estuaries and bays, or spread 

 along the shallows of sea-coasts. The vast series of ancient 

 deposits we are about to examine, are on the contrary 

 composed of regularly stratified rocks, with occasional 



