What evidence in rocks supports the seafloor spreading hypothesis?

Magnetite, a mineral found in basalt, the rock that makes up the sea floor, has particles in it which align themselves with the polar alignment of the earth (North and South). Every once in a while, in Earth's history, the polar alignment switches (North becomes South, South becomes North) and so do the magnetite particles. Thus, there are matching bands on each side of a spreading center where the magnetite has switched as the rock came out of the spreading center.