198 NEW YORK STATE MUSEUM 



less crystalline texture. There is however some confusion in the 

 use of the terms, and the same stone is occasionally known as 

 marble and limestone, e. g., the Lockport limestone or marble; 

 the limestone and coral shell marble of Becraft's mountain, near 

 Hudson; the Lepanto marble or limestone near Plattsburg, and 

 others. , 



The fossiliferous limestones are made up of the remains of 

 organisms which have grown in situ, as for example, the coralline 

 beds in the Helderberg and Niagara limestones, or have been 

 deposited as marine sediments. In the case of the latter the 

 fossils are more or less comminuted and held in a calcareous 

 matrix. Generally the fossil portions of the mass are crystalline. 

 The Onondaga gray limestone from near Syracuse, and the Lock- 

 port encrinal limestone are good examples. 



The fossil remains are less prominent and scarcely visible in 

 some of the common blue limestones, as in the lower beds of 

 Calciferous and in some of the Helderberg series. These rocks 

 are compact, homogeneous and apparently uncrystalline and un- 

 f ossilif erous. They are usually more silicious or argillaceous, that 

 is, they contain quartz or clay, the latter often in seams rudely 

 parallel with the bedding planes. On weathering, the difference 

 in composition is often markedly apparent at a glance. Similar 

 differences in composition are seen in 'the more crystalline mar- 

 bles, and are evident either by variation in color, or in the pres- 

 ence of foreign minerals, as mica, quartz, hornblende, pyrite, etc. 



The variations in the strength and durability is as great as in 

 the composition and texture. Some are stronger than many 

 granites in their resistance to crushing force, and equally endur- 

 ing; others consist of loosely cohering grains, and are friable and 

 rapidly dissolved by atmospheric agencies. The more silicious 

 and compact limestones are generally the more durable and 

 stronger; in the marble the well-crystallized and more homogene- 

 ous texture consists with endurance and strength. Both the mag- 

 nesian and dolomitic varieties are good stone as is proven by the 

 Calciferous and the Niagara limestones, and in the marbles of 

 Tuckahoe and Pleasantville, in Westchester county. 



