106 A PRACTICAL TREATISE 



through the practical experience of those who have either 

 actually tried its efficacy, or who have witnessed it in their 

 own neighbourhood. 



This ignorance of the distinguishing properties of marl has 

 necessarily led to many mistakes in its application, which 

 have occasioned the variety of opinions that are entertained 

 regarding its use. In most places where it was anciently 

 employed, and where its fertilizing influence was discovered 

 to be eminently great, it was thought by many farmers that it 

 could be made to supersede the use of dung; they, therefore, 

 in many instances, sold their hay and straw, and although, 

 notwithstanding this reduction of the quantity of putrescent 

 manure, they still for a time obtained large crops, yet, eventu- 

 ' ally, the chemical eflfects of the marl exhausted the land. No 

 second marling could operate upon it until it had been reno- 

 vated by repeated applications of dung ; and thus has arisen 

 the old saying, cited by Barnaby Googe, who wrote so long ago 

 as the middle of the sixteenth century, that 'lime and marl 

 are good for the father^ but had for the son.'' In this man- 

 ner, also, some valuable discoveries in agriculture have fallen 

 into disuse through their mistaken application, when governed 

 by local circumstances which were ill understood ; but wher- 

 ever marl of a kind adapted to the soil has been applied, and 

 that a judicious system of culture has been pursued, without 

 either over-cropping, or neglecting the use of putrescent ma- 

 nure, the proverb is so far from being well founded, that the 

 contrary may be safely affirmed. 



The common definition of marl given us by the best writers 

 on fossils, is, — that it is composed of clay, sand, and lime, very 

 intimately, but unequally mixed, slightly coherent, not ductile, 

 but stiflf, or viscid, when moist; most easily diffiisible in, and 

 disunited by, water, or even by exposure to the air, and by it 

 reduced to a soft, loose, incohesive mass — for the most part 

 competed of nothing more than calcareous earth — in which its 

 chief value consists — combined with a little mineral oil, clay, 

 and sometimes with ochre, or iron. It is also generally con- 

 sidered as a characteristic of marl, that it effervesces with 

 acids, though to that various exceptions have been discovered ; 

 from which it has been supposed that, wlien deprived of that 

 test, it contains no calcareous matter, yet it is found to pro- 

 duce ameliorating effects upon the soil.* Notwithstanding 



♦A bluish marl much used in some parts of Ireland, and long celebrated 



