what is the first material mentioned above comprise of?
A concrete mix, generally a coarse gravel or crushed rocks such as limestone, or granite, along with finer materials such as sand.
Concrete
Concrete is a composite material, comprising a matrix of aggregate (typically a rocky material) and a binder (typically Portland cement or asphalt), which holds the matrix together. Many types of concrete are available, determined by the formulations of binders and the types of aggregate used to suit the application for the material. These variables determine strength, density, as well as chemical and thermal resistance of the finished product.

Aggregate consists of large chunks of material in a concrete mix, generally a coarse gravel or crushed rocks such as limestone, or granite, along with finer materials such as sand.

what is fountain of time? It  is a sculpture by Lorado Taft where can you find that piece of work? In the Washington Park community area on Chicago's South Side which year did its sculpting first begin? May 1915 what materials were used to sculpt it? A form of hollow-cast concrete, reinforced with steel, which incorporated pebbles from the Potomac River.
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Concrete [SEP] Composition
For cementitious binders, water is mixed with the dry powder and aggregate, which produces a semi-liquid slurry that can be shaped, typically by pouring it into a form. The concrete solidifies and hardens through a chemical process called hydration. The water reacts with the cement, which bonds the other components together, creating a robust stone-like material. Other cementitious materials, such as fly ash and slag cement, are sometimes added—either pre-blended with the cement or directly as a concrete component—and become a part of the binder for the aggregate. Fly Ash and Slag can enhance some properties of concrete such as fresh properties and durability.