522 REPORT ON NATIONAL MUSEUM, 1886. 



Concretionary. Made of concretions, or rounded particles formed by the collecting of 

 mineral matter around some center so as to form a rounded mass composed of con- 

 centric layers like the coatings of an onion. When the concretions arc small, 

 like the roe of a fish, the structure is called oolitic, or if large as a pea, pisoliiic. 

 The best examples of this structure in our building stones are the oolitic lime- 

 stones of Bedford, Ind., and other places. A rare structure in crystalline rocks. 



Conglomerates. Fragments .stones composed of large, rounded fragments. 



Coquina. The Spanish name for a shell limestone which occurs abundantly in Flor- 

 ida, composed simply of a mass of shells connected together. 



Coral limestone. A rock composed of fragments of corals. 



Crystalline. Consisting wholly of crystals or crystalline particles, not frag mental. 

 Rocks which like granite or crystalline limestone arc made up wholly of crys- 

 talline grains are called crystalline-granular or granular-crystalline rocks. The 

 terms micro -crystalline and cryj)to-crystalline are often applied to rocks in which 

 the individual particles are too small to be readily distinguished by the unaided 

 eye. Such rocks are sometimes called compact, a term which is also applied to 

 fragmental rocks of similar texture. 



Curb. A flat piece of stone placed vertically, bounding the street edges of side- 

 walks, etc. 



Diabase. An eruptive rock composed essentially of a plagioclase feldspar and augitc. 



Dikes (or dykes). Masses of volcanic rock which have been forced up from below 

 in a molten condition to (ill fractures or fissures in the earth's crust. Such are 

 also called trap-rocks. The diabases and a variety of eruptive rocks frequently 

 occur in the form of dikes. 



Diorite. An eruptive rock composed essentially of a plagioclase, feldspar, and burn- 

 blende. 



Dip. The slope or pitch of the strata, or the angle which the layers make with 

 the plane of the horizon. 



Dolomite. A stone composed of mixed calcium and magnesium carbonates. 



A "Dry." A natural seam usually invisible when the rock is freshly quarried, but 

 which is brought out on exposure to weather or sometimes during the process 

 or cutting. A very serious defect in many stones. 



Escarpment. A nearly vertical natural face of rock or ledge. 



Feldspathic. Containing feldspar. 



Ferruginous. Containing iron oxides. 



Fibrous. Having a structure as though made up of bundles of distinct libers. This 

 structure is not found in any building stone, but is common in some forms of 

 gypsum and of calcite, which are used for making small ornaments. 



Flagstone. Any kind of a stone which separates naturally into thin tabular plates 

 suitable for pavements aud curbing. Especially applicable to sandstones and 

 schists. 



Flint. Quartz in any kind of rock is commonly known to quarrymen as flint. True 

 Hint is amorphous silica, occurring in nodular form in chalk beds. 



Foliated or schistose. Terms applied to rocks which, like gneiss and schist, have 

 their constituents arranged in more or less definite nearly parallel planes. 



Fragmental or clastic. Terms which are applied to rocks composed of fragments, 

 like ordinary sandstoue. When the fragments are the size of a pea or larger, 

 and rounded in form, the structure is called conglomerated, or if the particles 

 are angular, orecciated. 



Freestone. This is a term which has been applied to stones that work freely in any 

 direction. Especially applied to sandstones and limestones. A term of no spe- 

 cial value, as it is too indefinite. 



Gneiss. A rock of the composition of granite but in which the ingredients are 

 arranged in more or less parallel layers. 



Gneissoid. Like gneiss. 



Grain. The direction in a rock at right angles with the rift. 



