The remarkable fit that was obtained was more precise than even these researchers had expected / As shown in figure 7.3 there are a few places where the continents overlap / Some of these overlaps are related to the process of stretching and thinning of the continental margins as they drifted apart / Others can be explained by the work of major river systems. / For example since the breahup of Pangaea the Niger River has built an extensive delta that enlarged the continental shelf of Africa.