l82 NEW YORK STATE MUSEUM 



of lime carbonate from solution. The formation of limestone by 

 similar methods is going on today along the sea coast, as exemplified 

 by the shell beds, coral reefs and calcareous muds which are widely 

 distributed and which require only consolidation from the weight of 

 overlying strata and uplift from the sea to convert them into lime- 

 stones similar to those exposed in the early Paleozoic formations 

 of New York State. The deposition of lime carbonate in quantity 

 also takes place in fresh waters ; the beds of marl found in many 

 swamps and lake basins of this section are the result of precipita- 

 tion of lime which has been brought in by tributary streams and 

 springs, the lime being thrown out of solution sooner or later T)y 

 evaporation of the waters or through the agency of plant growth. 

 There are many thousands of acres of these surface marls in the 

 central and western parts of the State. 



The conversion of common limestone into marble requires great 

 pressure, which in nature is developed through those crustal move- 

 ments that lead to the formation of folded mountains ; under the 

 stress thus exerted, accompanied by heat and probably in the pres- 

 ence of moisture, the lime carbonate behaves like a mobile or plastic 

 substance and is able to assume its proper crystal character, that 

 of calcite. Each particle becomes a complete crystal, with the char- 

 acteristic cleavage, optical properties and other features of calcite, 

 though owing to the space limitations it can not assume the outward 

 regularity of form which belongs to calcite when free to expand in 

 all directions. The change, or metamorphism, is accompanied also 

 by a rearrangement and crystallization of the impurities, as has 

 already been noted. 



There are two areas in New York where crustal movements have 

 taken place on a great scale during past geological ages. The 

 Adirondacks in the north are a part of the old Laurentian highland 

 which was uplifted in early Precambric time and subjected to great 

 vicissitudes of compressive folding, faulting and invasions by 

 igneous rocks before the regular stratified formations began to be 

 deposited. In the southeast is the Highlands-Taconic region, of 

 which the Highlands proper represent a part of the old Appalachian 

 highland of Precambric age, and the Taconic a later uplift that came 

 at the close of the Ordovicic period. 



THE ADIRONDACK SECTION 



The crystalline limestones of the Adirondacks appear in belts, 

 elongated in a general northeast-southwest direction parallel to 



