We have re-examined the question of whether it is generally true that in continental regions a relatively magnetic crust overlies a relatively non-magnetic mantle. Whereas the original conclusion was based on limited data, the present study is based on about 400 globally-distributed xenolith samples. While it is now clear that the ''Moho'' represents a maximum velocity gradient in a complex transition from the crust to mantle, and while crustal magnetization is highly variable, the original concept of a ''magnetic crust'' overlying a non-magnetic mantle is strongly supported by the new data. A large upper mantle xenolith suite of ultramafic composition is characterized by non-magnetic chrome spinels and magnesian ilmenites. Such rocks are magnetic only where demonstrably altered. The most significantly magnetic rocks within the crust are mafic types prograded to granulite grade or mafic melts of basaltic composition which crystallized deep in the crust at high pressure and temperature. Prograded rocks have characteristic magnetite Curie points, and are strongly magnetic, especially the more mafic compositions, while the mafic rocks formed by crystallization at depth have Curie points between 400¿--570¿ C and are strongly magnetic.

Induced magnetizations are commonly several A/m, and can readily account for long-wavelength magnetic anomalies measured by satellite and aircraft; thus, there is no need to search for exotic sources for ''missing'' crustal magnetization. No metal or other peculiar magnetic species have been observed by us in any of our (unaltered) samples. Mineal assemblages (including magnetic components) are consistent with oxidizing conditions close to the FMQ buffer.