What kind of rocks have pebbles in it

The pebbles can be made of quartz or some other mineral. It is glued together with iron oxide, calcium carbonate, or silica. It looks lumpy with bigger rocks cemented with small gravel and sand. 
I believe this is the answer.

The speed of  sound:   sound travels  at different speeds depending on what it istraveling through. of the three mediums (gas, liquid, and solid)  sound waves travel the slowest through  gases, faster  through  liquids, and fastest  through  solids.

Yes they are correct good day