CALCARKOUS MANURES— APPENDIX. 303 



while others, close to its border, but in a diiTerent direction, or on a different 

 level, mi.trht escape its influence. 



Objection 2. — There is not enough difference in the usual or average 

 healthiness of families the most exposed, and others the least exposed to 

 mill-ponds, to attribute much of the effects to these causes. Whole neigh- 

 borhoods, in some autumns, are very healthy, and in others very sickly, 

 without either condition seeming to be connected with any certain and 

 known state of the nearest mill-ponds. 



A^isiver. — The extreme lightness of 'the poisonous air, and great and fre- 

 quent variations in the direction, force, and continuance of the winds on 

 which it is borne, make it generally impossible for it to be known from 

 which particular pond or ponds«the malaria rises, or where it is carried. It 

 is most probable that the exhalations of twenty ponds, of which the most 

 remote may be thirty miles apart, may be mingled together by the winds 

 of a single day, and thus combine and average the effects of all. Further, 

 if all the mill-ponds of a county furnish one half of the active and injurious 

 malaria, and the other half is thrown off, nearly equally, by the whole 

 surface of the land, (though some parts would receive the strongest doses, 

 and others escape with having only the weakest,) it would be impossible 

 to understand the mode, and estimate the intensity of operation of the 

 known general causes; or to refer, with certainty, any one effect to its 

 special or principal cause. Thus, a farm relieved from all malaria of its 

 own product, by marling and by drying its mill-pond, though evidently 

 showing the benefit in increased general healthiness, might still be sorely 

 visited by the seeds of disease from other and remote sources, directed and 

 concentrated by a steady wind. 



Having presented these views of the origin, action and effects of malaria 

 in this country, I can better exhibit the progress of the causes which I 

 believe to have operated, and which are still continuing to operate, to pro- 

 duce the change from a healthy to an unhealthy state. 



When our ancestors first reached this shore, nearly the whole country 

 was in a state of nature. The savages had cleared for cultivation but a few 

 fertile spots on the banks of the rivers ; all the remainder of the land was 

 under one great forest. The streams had not been obstructed by the cutting 

 down of trees across their beds, (by which in many cases streams have 

 since been choked, and swamps thereby formed, or greatly extended.) No 

 dams had obstructed the free and regular course of the streams, and there- 

 fore no great artificial floods were formed. The soil not having been 

 cultivated, was not exposed to be washed away by the rains into the rivers. 

 The waters therefore were generally clear, instead of being generally 

 muddy, as since all these circumstances have been changed. In this former 

 state of things there could have been existing but few sources of malaria. 



The first formation of sources by the civilized settlers, was in making 

 ponds to supply mills. But while these were yet few in number, the con- 

 structers of course chose the best and most unfailing streams; and the 

 ponds were also, for a long time, surrounded by dense and tall forests. Such 

 hilly land as the margins of the ponds would certainly not be brought into 

 cultivation while so much that was far better, and easier to till, remained 

 unoccupied. Hence, such ponds produced but little malaria, and that little 

 was warded off from the settlers, or taken up by the forest growth. The 

 general wooded state of the country, also, for a long time, rendered the 

 supplies of water more regular, and prevented the severe droughts, which 

 would have altered greatly, as is usual now, the levels of the ponds. 



The clearing, cultivation, and consequent washing of the lands of the 

 upper country, greatly increased the muddiness, and quantity of alluvial 



