24 THE MOnERN PERIOD. 



an.l other upland plants, the seeds of which must have been washed 

 into the sea by streams and deposited with the mud. 



The low or inner marsh, which I have previously mentioned 

 under its other names of blue marsh and corky dike, is much less 

 valuable than the red. It contains, however, much more vegetable 

 matter, and sometimes approaches to the character of a boggy swamp ; 

 so that when a quantity of it is taken out and spread over the upland, 

 it forms a useful manure. It emits a fetid smell when recently turned 

 up, and the water oozing from it stains the ground of a rusty colour. 

 It produces in its natural state crops of coarse grass, but when broken 

 up is unproductive, with the sole exception that rank crops of oats_ 

 can sometimes be obtained from it. 



The chemical composition of this singular soil, so unlike the red 

 mud from which it is produced, involves some changes which are of 

 interest both in agriculture and geology. The red marsh derives its 

 colour from the peroxide of iron. In the gray or blue marsh, the iron 

 exists in the state of a sulphuret, as may easily be proved by expos- 

 ing a piece of it to a red heat, when a strong sulphurous odour is ex- 

 haled, and the red colour is restored. The change is produced by the 

 action of the animal and vegetable matters present in the mud. These 

 in their decay have a strong affinity for oxygen, by virtue of which 

 they decompose the sulphuric acid present in sea- water in the forms 

 of sulphate of magnesia and sulphate of lime. The sulphur thus liber- 

 ated enters into combination with hydrogen, obtained from the organic 

 matter or from water, and the product is sulphuretted hydrogen, the 

 gas which gives to the mud its unpleasant smell. This gas, dissolved 

 in the water which permeates the mud, enters into combination with 

 the oxide of iron, producing a sulphuret of iron, which, with the 

 remams of the organic matter, serves to colour the marsh blue or gray. 

 The sulphuret of iron remains unchanged while submerged or water- 

 soaked ; but when exposed to the atmosphere, the oxygen of the air 

 acts upon it, and it passes into sulphate of iron or green vitriol, — a 

 substance poisonous to most cultivated crops, and which when dried 

 or exposed to the action of alkaline substances, deposits the hydrated 

 brown oxide of iron. Hence the bad effects of disturbing the blue 

 marsh, and hence also the rusty colour of the water flowing from it. 

 The^ remedies for this condition of the soil are draining and liming. 

 Drammg admits air and removes the saline water ; lime decoinposes" 

 the sulphate of iron, and produces sulphate of lime and oxide of iron, 

 both of which are useful substances to the farmer.* 



* Since the publication of tlie first edition of this work, the blue marsh of Nova 

 bcotia has been extensively improved by this process. 



