276 Correspondence. 



ness becomes known, and may be represented by the amount of the 

 weight. For the harder minerals, it would probably be necessary to 

 replace the steel by a diamond properly set ; but for the purposes I 

 have in view, in testing the relative hardness of the usual building ma- 

 terials, I think the steel will suffice. The model I made appeared to me 

 to act very well in the trials I made of it. Do you think the instru- 

 ment might be used with confidence, or do you detect any thing fal- 

 lacious in it ?" 



Extract of a Letter from Captain Campbell, Assistant Surveyor General, 



Madras. 



In my remarks about fever I should have mentioned, that it is com- 

 monly known, and I have had opportunities of seeing that it is a fact, 

 that the people of the hills of the mountainous tracts of Kimedy and 

 Goomsoor, suffer from fever when they descend to the plains and re- 

 main there for ten or fourteen days, quite as severely as the people of 

 the plains suffer from the climate of the hills ; and I have been informed, 

 that the hill people of the Table lands of the Salem district, dislike 

 descending and remaining in the plains below for the same reason. 



I have sent you a paper on Petrefaction, published originally in the 

 Madras Spectator, which is very interesting, and I hope you will think 

 it worth republishing. It is I believe, translated by an officer in the 

 Madras 8th Cavalry, from whom I hope we may have more of the same 

 kind. You will observe the bearing the subject has upon speculative 

 Geology, in accounting at once for the association of trap rocks 

 and silicified wood, without " outbursts of thermal waters holding- 

 silica in solution," and such other wild speculations, which are particu- 

 larly unfortunate, as such waters have in no case ever been known to 

 silicify any thing, as in the Geysers of Iceland, where the only effect 

 they produce is incrustation. 



The paper was published in reply to some remarks of mine, doubting 

 the organic origin of the " woodstone" of Trivicary, in which, misled 

 by the compact appearance of some specimens I had seen, and not 

 being aware that any trace of the organic structure remained, I denied 

 the sufficiency of the evidence derived from outward form and appear- 

 ances as a proof of organic origin. In doing so, I roused the ire of 

 some disputants ; but fortunately for the interests of science, as Mr. 

 Kaye informs us in the Madras Journal, his attention was given in 

 consequence to the search of further evidences in organic associations, 

 from whence has resulted the interesting discovery of the fossiliferous 



