308 MARL. 



ter, and the ice, expanding with almost irresistible force, separates 

 the particles, which cohere, indeed, so long as the frost continues, 

 but fall away from one another on the first thaw, by which the solid 

 rock of the autumn and winter becomes a heap of dust in the spring. 

 In the same way, we see chalk, exposed to the wet and the frost, 

 fall down to powder, and, in virtue of this property, and its constitu- 

 tion as carbonate of lime, employed with perfect success in lieu of 

 lime and marl. Wherever there is a bed of chalk at hand, it is need- 

 less to go further in search of marl and quick-lime, in so far at least 

 as the calcareous principle is concerned. 



Argillaceous marl and sandy marl must, of course, act in two 

 different ways upon the soil : in virtue of the calcareous element in 

 either case, and in virtue of the argillaceous principle in the one, 

 of the sandy principle in the other ; and the kind of soil for which 

 they are severally adapted can be conceived beforehand. To a stiff, 

 clayey soil, we would naturally add the sandy marl; to a light sandy 

 soil we would supply the argillaceous product, and thus effect im- 

 provement by a kind of double tide. It is therefore very important to 

 distinguish between these two effects produced by marl — one me- 

 chanical, connected with the presence of clay or sand ; the other 

 chemical, and depending on the presence of carbonate of lime. It is 

 to these two effects, separately and combined, that all the influence 

 of marl is usually ascribed by practical agriculturists. From certain 

 inquiries common to M. Payen and me, however, it appears that 

 marl must act in yet another way ; our analyses show that it always 

 contains a certain though variable proportion of azotized matter. 

 And there is nothing extraordinary in the discovery of this fact ; it 

 is no more than might have been anticipated from the ge(^ogical cir- 

 cumstances attending its production. Marls are, as has been said, 

 always connected with the most recent formations of the tertiary 

 series ; they are constantly accompanied by remains, which attest 

 the presence of organic beings, and frequently they consist of little 

 else than shells, and the disintegrated dwellings and bodies of mo- 

 luscas, and madrepores, and corallines, and other inferior forms of 

 things that once had life. It is by no means astonishing, therefore, 

 that deposites which have had such an original should still contain 

 evidences of the presence of the softer and more decompoundable, as 

 well as of the harder and more rebellious constituents of the beings 

 to whose existence they are due. One sample of marl which we 

 analyzed, gave 0.002 of azote ; another, from the Lower Rhine, 

 gave rather more than 0.001 of the same element. It were, there- 

 fore, very proper, in analyzing marls, chalks, &c., to have an eye tc 

 their organic or azotic, as well as to their mineral constituents ; there 

 can be very little question of the azotized elements being at the bot 

 torn of the really wonderful fertilizing influences of the marls of 

 certain districts. 



Marl ought, like lime, to be spread very evenly over the land ; i 

 is generally laid on in the same way as lime — in little heaps at re 

 gular distances, and then scattered abroad. It appears to be a verj 

 general opinion that it is not advisable to cover it immediately, or verj 



