If five layers or beds of stone are to be properly tested, then five samples must be taken, _one broken from each layer of solid rock in place_. The five layers may have the same color, or look much the same, but fine grains of sand, hardly visible without magnification, may be abundant in some layers and not in others. If circumstances do not permit having five different tests made, but allow only one sample to be run, then specimens should be taken from all five beds, their sizes being in proportion to the relative amounts expected to be quarried from each bed, and all five specimens sent to the analyst, who can crush and mix them. A single grab sample taken from loose rock on a hillside, in expectation that it will represent the rocks inside, depends as much on luck as betting on the weather next 4th of July, a year hence. The chemist who analyzes the limestone for calcium can usually report on the kind of impurity if he will take the time to do it. “Cotton Rock” Limestone “Cotton rock” refers to a white to slightly gray or buff variety of limestone which has a “soft”, somewhat chalky and porous appearance that is suggestive of cotton. Missouri “cotton rock” is usually dolomitic. Although the term “cotton rock” has no standing in a technical sense, its fairly wide use indicates that the name has descriptive value. Marble Marble, in a scientific sense, is a metamorphic rock and does not occur as such in Missouri. However, marble has been used as a name in commercial trade to refer to a crystalline, fairly pure limestone, which possesses most of the useful qualities of true marble. In that sense the “marbles” quarried near Ozora and Carthage, Missouri, are very excellent stone. No doubt some recrystallization has occurred in connection with the faulting in the Ozora region, and this may be interpreted as mild metamorphism. The Carthage “marble” is quarried from beds of limestone well developed for structural purposes. These “marbles” effervesce in acid, of course, just as described for limestone. In this connection it is interesting to note that the polish on limestone or marble is not durable where exposed to the weather in the same sense as is the polish on granite. Because limestone and marble are softer than granite they may be cut and polished at lower cost, but because of their ease of attack by acid, water, and abrasion they soon become dull when used as an exterior stone. For interior decoration they are excellent, of course. Granite contains hard minerals which happen not to be attacked appreciably by dilute acids, and therefore it retains a polish for a long time even where exposed to the weather. Cave Onyx and Deposits