Looks like small rocks cemented in between poured concrete layers, The poured concrete would have a "hole" in the center at the time of pouring, and they probably used newspaper or some other material in the concrete to create air pockets. The newspaper would be burned out later. Use mortar to attach the rocks and "voila". I'd recommend doing the mortar step in place, as it would be very heavy to move. Basic fountain instructions (pumps, piping, etc.) can be found all over the web. It doesn't look too difficult.