1838.] 



On iJic Laieritic Formation. 



337 



ber of this Journal will be found a paper by Mr. Cole, in vv'bich be states 

 with great clearness the variety of opinions entertained upon the forma- 

 tion of the laterite, and where he calls upon those who may have tra- 

 versed the localities where it abounds, to give their ideas thereon. Having 

 lately visited Coorg, the Neilgherries, the Western Ghauts and Coast, I 

 have been led in the jjresent paper to record my veiy humble viev^'s. 



To the excellent paper of Mr. Cole, I refer those interested on the sub- 

 ject, for the desoriptive characters of the laterite, and for the many ideas 

 ■entertained on it by all Indian geologists. It is by an mialysis of what 

 is written that we can alone discover wdiatis truly known, and in this way 

 truth gets filtered from all erroneous impurities. As the decomposition of 

 rocks containing much hornblende into lithomarge is not confined to tha 

 Neilgherries, but takes place op the western coast, and in many places 

 in IMysore, besides other localities where cold and frost and elevation do 

 not operate, we mast look to other causes, different to those hinted at by 

 Dr. Benza. I think it will be observed, that where lithomarge and laterite 

 abound, for they ai'e frequently associated, the rocks whose decomposition 

 form these two states, are feiTuginous — ^veins of iron ore are found im- 

 bedded in both, and the quartz, entering into the formation of these 

 ro iks, is at the same time highly ferruginous. This greater proportion 

 thtm usual of iron in the rock would dispose quickly to its decora- 

 position, and account for a bed of laterite or a small hill of lithomarge 

 without calling in the assistance of frost, elevation, &c., or the hidden 

 and disturbing forces of by-gone centuries. All along the western coast, 

 near Cannanore, lithomargic hills and lateritic rocks are associated, 

 and even the passage of one into the other is sometimes seen, as in the 

 lithomargic earth on the Neilgherries, an excellent specimen of which 

 is preserved. Some short time after I began to see the connection be- 

 lv,-een the lithomargic and lateritic formation, I was gratified by read- 

 ing a remark of Dr. Heyne, where he says, lithomarge is a sure sign 

 of being near a bed of iron-stone. It would be perhaps as difficult to 

 define the characters of lithomarge as laterite; and here again is ano- 

 ther point in common ; for as both are the result of decomposition, they 

 must vary much in appearance. Hence no two authors agree in their 

 description of the widely difiused laterite. The laterite of one is 

 scarcely that of another, and the specimens from one locality dilfer much 

 from those of another. This might arise either from a greater or less 

 proportion of iron, and the oxydation thus resulting, or it might be re- 

 ferred to the preponderance of the quartz over the felspar, or the felspar 

 over the hornblende. A rock consisting principally of hornblende and 

 felspar, I imagine would decompose into lithomarge, and one containing 



