* kokopoulos knew that early iron age cultures had appeared in east africa within a few centuries of their spread south along the valleys of the blue and white nile and down along the great rift wall and into its volcanic heartlands and hinterlands where the settled tribes in the fertile foothills of the range of the aberdares , mount kenya , the ruwenzori mountains and mounts mbulu , meru and kilimanjaro flourished to his day .