586 PRINCIPLES OF STRATIGRAPHY 



Lucknovv; which Hes approximately midway between the Indus and 

 the Ganges headwaters and about 370 feet above sea-level. It 

 abounds in gravels and conglomerates near the sloping borders, but 

 lutaceous or clayey deposits, more or less arenaceous, prevail over 

 much of the plain, especially near the center, with only subordinate 

 deposits of sand, gravel, and conglomerates. Beds of blown sand 

 of great thickness are found in some regions. Pebbles are scarce 

 at a distance of more th.an twenty or thirty miles from the enclosing 

 hills. Shells of river and marsh molluscs are occasionally found, 

 and calcareous concretions and nodules of irregular shape, locally 

 known as kankar, are frequent. "The more massive forms 

 are a variety of calcareous tufa, which sometimes forms thick beds 

 in the alluvium and frequently fills cracks in the alluvial deposits, 

 or in older rocks." (OIdham-4o:^J7.) Calcareous tufas also .form 

 conglomerates in the stream beds by cementing pebbles derived from 

 the hills. In the clays along the borders and in the shoals of the 

 Jumna River a great variety of vertebrate remains has been found, 

 including elephant, hippopotamus, ox, horse, antelope, crocodile, 

 and various fish. Borings in other regions revealed the presence of 

 peat, forming extensive beds to a depth of 20 to 30 feet below 

 the surface, wdiile a layer of stiff blue clay 15 feet in thickness was 

 found 10 feet below the surface at Calcutta. Clay and variegated 

 sand with calcareous concretions, mica and small pebbles alternated 

 to a depth of 120 feet, below which a quicksand was found. At 

 152 feet this became dark and coarse of grain and intermixed with 

 red water-worn nodules of hydrated iron. At 159 feet a stifif clay 

 was found which, at 163 feet, became friable and contained much 

 vegetable and ferruginous matter. Lower, still fine and coarse sands 

 alternating with clays occur, while at 340 feet a ruminant bone 

 was found, and pieces of tortoise shell at still greater depth. Three 

 hundred and ninety-two feet below the surface pieces of coal, such 

 as are found in the mountain streams, and fragments of decayed 

 wood were found in the sand, while below 400 feet sand and 

 shingle of fragments of primary rocks abounded. The borings 

 also showed wood, remains of terrestrial mammals, fluviatile reptiles, 

 and fresh-water molluscs. No traces of marine fossils have been 

 found. The presence of earthy limestones in these deposits is of 

 especial interest, because it shows that limestones do not necessarily 

 indicate lacustrine or marine conditions. As already noted, in 

 northern Mexico and other tropical regions of America, a super- 

 ficial crust of white lime, often free from foreign material, is 

 formed. This material, called tepctate, has been dissolved from 

 the limestones of the surrounding region, transported in solution by 



