Magnetic Studies of Rocks and Sediments— -Belshe 
395 
tion was obtained in the sample taken above 
this level. Thus, the material which was closest 
to the basalt and which should have been heated 
by it to produce a thermo-remanent magnetiza- 
tion in accordance with that of the basalt, did 
not show this effect. 
This pattern of magnetic polarizations pre- 
sents a paradox. The facts might be interpreted 
by three hypotheses: (1) The material nearest 
the basalt might have become unstable, or per- 
haps was altered by processes emanating from 
this igneous body, and acquired its field more 
recently. (2) The positive direction indicates a 
period of normal magnetizations which was 
typical of the time at which the basalt was 
intruded; subsequent to this, a period of re- 
versal occurred during which the overlying re- 
versed materials were laid down and exsolu- 
tion products in the basalt caused the acquisi- 
tion of a now reversed remanent magnetiza- 
tion. (3) The reversed magnetization of the 
basalt may be an example of a spontaneous self- 
reversal occurring during a period which is 
better documented by the positive inclination of 
the immediately overlying and thermally mag- 
netized sedimentary material, remagnetized by 
the intrusion from its original reversed polari- 
zation which is still retained to within 1 m of 
the contact. 
Even on the assumption that the basalt is 
but little thicker than the maximum depth to 
which it was penetrated by the drill, we cannot 
consider the sampling available sufficient to 
permit a conclusive study of the manner of de- 
crease of thermo-remanent magnetizations 
away from the contact. 
These studies indicate two points that should 
be taken into consideration in planning any 
later deep drilling operations. First, it is ex- 
tremely important for these studies that some 
attempt be made to orient the core. The writer 
discussed this point at great length with people 
in the office of the AMSOC committee (of the 
Division of Earth Sciences, National Academy 
of Sciences) during the period of preparation 
in I960 for 'the "Cuss IF’ operations. Unfortu- 
nately, the intent expressed then to orient all 
cores was not realized. Second, it is extremely 
important in studies of this type that recovery 
be as complete as possible, even in the sedi- 
mentary column. 
A further matter for consideration has come 
from studies of these "Cuss II” drill samples. 
This concerns the consolidation characteristics 
and porosity of the sediment as studied and 
reported by Hamilton (1964) and by Moore 
(1964). Hamilton shows that porosities at the 
sediment surface were about 80 per cent and 
that in situ porosities for the deepest samples 
were of the order of 72 per cent. Thus, a reduc- 
tion of no more than 5 per cent due to overbur- 
den pressures could be accounted for even in the 
deepest sample studies (168 m). Moore shows 
that the shear strength varied from less than 
0.1 kg/cm 2 at the surface to more than 2.8 
kg/cm 2 near the basalt. 
These findings have two points of impor- 
tance to studies of magnetism. First, the in- 
crease in shear strength seems to be due to dia- 
genetic processes such as cementation and 
bonding. These processes might be important 
in the acquisition of chemical magnetizations 
during the consolidation history of marine sedi- 
ment, particularly in an area where iron ce- 
mentation might be expected. Second, these 
studies in no way support the suggestion made 
by Keen (1961), working with the writer at 
Cambridge University, that compaction might 
produce an inclination error which would in- 
crease with burial depth in samples taken by 
piston coring. 
The deep marine magnetic studies being 
done by the Hawaii Institute of Geophysics, 
in addition to studies of Hawaiian basalt, 
should continue to have immediate relevance 
to the Moho Hole drilling project. Our meas- 
uring equipment and techniques are eminently 
suited to this task. One particular area to 
which we can contribute comes from the 
knowledge we have acquired in successfully 
constructing a photographic recording instru- 
ment which can orient a deep-sea sediment 
core. 
REFERENCES 
Belshe, J. 1962. Magnetic properties of some 
sediment cores. J. Geoph. Res. 67 : 3541-3542. 
