MINERAL RESOURCES OF THE STATE OF NEW YORK I45 



References 

 Beck, Lewis C. Mineralogy of New York, 1842 

 Dale, Nelson C. Postglacial Manganese in Columbia county, N. Y. N. Y. 



State Mus. Bui. 207-208; 1919, p. 85-100 

 Mathe:, W. W. Geology of the First Geological District, 1843 



MARL 



Marl is an unconsolidated limestone. Its description seems to 

 justify a separate article for the reason that it is quite independent 

 of the hard limestones in areal distribution, has a different method 

 of occurrence, and its physical properties do not permit the same 

 extended uses to be made of the material as of limestone. 



Chemically marl usually ranks with the high-calcium limestones. 

 The proportion of lime carbonate is often well above go per cent, 

 that is calculated on a water-free basis. When freshly dug it has 

 a large moisture content, practically equal in weight to that of the 

 marl itself; the water may be dispelled by prolonged drying in the 

 air or more rapidly by exposure to the higher temperature of a kiln, 

 since it is all mechanically held. Admixture with a little clay is 

 common, also not infrequently with sand, so that small proportions 

 of silica and alumina are usually shown by analysis. The magnesia 

 content seldom exceeds i per cent. 



The marls of New York are of recent and present day formation. 

 They are found in surface depressions, associated with other uncon- 

 solidated materials and especially with peat, which often occurs on 

 top of the marl. Swampy areas and shallow ponds and lakes fre- 

 quently contain deposits. Whenever waters accumulate on the 

 surface, the dissolved lime brought in by springs and streams may 

 precipitate by evaporation and escape of the solvent carbon dioxide, 

 a process that is facilitated by increasing warmth of the waters. 

 The lime carbonate is also abstracted by shell organisms and by 

 minute plant forms. In some instances the lime is deposited directly 

 by springs and streams before the waters reach the collecting basin 

 as tufa or travertine, which forms an incrustation on vegetable 

 growth — mosses and grasses. Marls contain more or less shell 

 remains of the organisms that abound in fresh waters and these may 

 constitute a considerable proportion of the deposit, if not exceeding 

 in amount the granular lime. 



Occurrence. The more extensive marl deposits are in the central 

 and western parts of the State. The large share which limestones 

 have in the geological structure of that section contributes to their 

 formation by supplying abundant calcareous material for solution 



