Br Kelaart's Notes on the Geology of Ceylon. 29 



admit of classification. 1. Laterite, properly so called, of a 

 hard, compact, almost jaspedeous rock, formed of indurated 

 clay, tubular or sinuous, in which are impacted quartz cry- 

 stals of various sizes and colours ; generally of a reddish or 

 brick colour. To this kind, the term Quartzose may be 

 applied, as it contains a larger proportion of undecomposed 

 quartz. The cavities and sinuosities are lined or sometimes 

 filled with a whitish, yellowish or reddish clay. 2. A second 

 variety of laterite, and that most frequently met with in 

 Ceylon, is of a softer consistence, and can be cut easily with 

 a knife, but hardens on exposure to the atmosphere. The 

 terra Lithomargic laterite has been applied to this kind. 3. 

 There is another form, which my friend Staff-Surgeon Dr 

 Clark calls Detrital. This is found in nullahs or ravines. It 

 is evidently formed of pebbles of quartz, loosely imbedded 

 in clay, both being washed down to these nullahs by the heavy 

 rains. The detritus of laterite is seen about Colombo form- 

 ing a braeccia with marine shells. A laterite gravel is also 

 seen in various parts of the island, covering the laterite hills, 

 and it is also found at their base. This gravel is nothing 

 more than the quartz crystals of the lateritic rocks, separated 

 by the rains from their clayey matrix. Some of the pebbles 

 are denuded entirely of the clayey covering ; others retain 

 still a thin coating of it. Lithomarge is a sectile clayey sub- 

 stance of variegated colours. It is chiefly formed of a de- 

 composed felspar and hornblende ; whitish when the former 

 prevails, and yellow or reddish when hornblende predomi- 

 nates in the rock from which it is derived, owing to the 

 larger proportion of oxide of iron which the latter mineral 

 contains. There are extensive hills of lithomarge in Ceylon, 

 and frequently it lies* under the hard laterite, and is often in- 

 terposed between its layers. 



With the exception of Voysey, and his few supporters (who 

 regard the laterite to be of igneous or volcanic origin), geo- 

 logists consider laterite to be the product of the disintegra- 

 tion and decomposition of granitic rocks. The difference of 

 opinion rests upon the question, whether the disintegration 

 or decomposition took place in situ, or whether the disinte- 

 grated masses were deposited, or brought from a distance, 



