1836.] 



Laterite, or Iron Cldtj, 



103 



away until they are decomposed ; on the contrary, water seems to per- 

 colate through the mass, and carry off the other constituents of the 

 sienite, leaving the felspar in a decayed state in mass." 



I have now to advert to a mention of this rock by the celebrated 

 Voysey — a name so famed in the history of Indian geology, that I 

 hesitate in delivering an opinion, which is at variance with his notion 

 of the origin of the laterite. The following passage is extracted from 

 a paper dated so long ago as 1820, though only given to the world 

 in 1833.* 



" The basalt, which covers the granite to the N. W. of Hyderabad, 

 at first appears only on the summits of some of the hills ; the latter 

 rock still occupying the vallies and forming the sides of the moun- 

 tains. It afterwards gradually increases in extent, until it covers it iti 

 all its parts, and granite re-appearing only in the beds of some of the 

 rivers, and forming the base of some isolated peaks. It is sometimes 

 found columnar, the columns being of all sizes, from a foot to a yard 

 and a half in diameter, as at Oudghir, Monegal, &c. It varies from a 

 very compact semi-crystalline rock, resembling hornblende rock, to a 

 porous basalt, which passes into wacken, containing stilbite, mesotype, 

 ic thy oph thai m i te, heliotrope, calcedony, green earth, quartz with 

 crystals of calcarious spar imbedded, the form of which the quartz has 

 taken, demonstrating that this mineral has been the last deposited. 

 The wacken passes into iron clay in the space of a few yards. The 

 latter forms elevated table-land at Beder, which is 2,359 feet above the 

 level of the sea; it closely resembles that of the Red Hills at Madras, 

 Nellore, Singhirikunda (in the two latter on granite), all on the sea 

 coast, but in this instance rests on basalt. I observed in it plumb blue 

 lithomarge, and pisiform iron ore." 



Now, if by the iron clay, mentioned in this passage, is intended the 

 laterite of Buchanan, we must understand the author to attribute one 

 mode of origin to that rock, to the basalt and to the wacken, not only 

 in the Hyderabad country, but in the three other localities, where the 

 mineral is said to prevail " closely resembling" that near Hyderabad. 

 Here then, we may presume, is the authority for considering laterite 

 as " associated with the trap formation." In Mr. Calder's paper on 

 the geology of India, the same character is, indeed, given to this 

 mineral ; but as that writer offers no independent proof of his own, 

 but acknowledges having availed himself of Dr. Voysey 's unpublished 

 journals, we may presume that he is only stating the opinions of the 

 latter author. The passage I have alluded to in Mr. Calder's paper is 

 as follows. " This trap formation is observed to terminate on the sea 

 coast, a little to the north of Fort Victoria, or Bankot, where it is suc- 

 ceeded by the iron clay or laterite (a contemporaneous rock associating 



* Journal of the Asiatic Society of Bengal for August 1833, p. 4C0, 



