THE MINING AND QUARRY INDUSTRY IQI2 79 



a silicate of magnesium and iron, and is therefore not related to 

 the varieties already described. Ophitic limestone, or ophicalcite, 

 is a crystalline limestone or dolomite carrying grains and nodules 

 of serpentine scattered more or less evenly through its mass. Its 

 ornamental quality lies in the speckled or mottled pattern and the 

 sharp contrast between the clear white ground mass and the greenish 

 serpentine inclusions. 



Marbles belonging to these various types find representation in 

 the geologic formations of the State and are quarried on a com- 

 mercial scale or have been so quarried in the past. 



The true or crystalline varieties are limited in occurrence to the 

 metamorphic areas of the Adirondacks and southeastern New York. 

 They are of early geologic age, antedating the period of crustal 

 disturbance and metamorphism which in the Adirondacks was 

 brought to a close practically long before Cambric time and which 

 in southeastern New York was completed in the Paleozoic. This 

 thoroughly crystalline character is in fact a development of the 

 strong compression accompanied by heat to which they have been 

 subjected; having been originally, no doubt, ordinary granular or 

 fossiliferous limestones similar to those so plentifully represented 

 in the undisturbed formations outside the regions. 



The crystalline limestones of the Adirondacks are most abundant 

 on the western border in Jefferson, Lewis and St Lawrence counties 

 where they occur in belts up to 4 or 5 miles wide and several times 

 as long, interfolded and more or less intermixed with sedimentary 

 gneisses, schists and quartzites. They are found in smaller and 

 more irregularly banded areas in Warren and Essex counties on 

 the eastern side, but have little importance elsewhere. The ophitic 

 limestones that have been quarried at different times belong to the 

 same series. The marbles of the Adirondacks comprise both the 

 calcite class with very little magnesia and the dolomite class con- 

 taining high percentages of magnesia. No definite relation is ap- 

 parent in regard to the occurrence of the two and both may be 

 found in the same area and in close association. 



The southeastern New York marbles occur in belts which follow 

 the north-south valleys, east of the Hudson, from Manhattan island 

 into Westchester, Dutchess and Columbia counties. They range 

 from very coarsely crystalline to finely crystalline rocks, are prevail- 

 ingly white in color and belong to the dolomite class. They are 

 interfolded with schists and quartzites, the whole series having steep 

 dips like those of strongly compressed strata. The geologic age 



