Magnetic Spherules — Pettersson and Frederiksson 
75 
Fig. 2. Polished sections of black spherules. A, spherule from Core 71, about one meter below the sediment 
surface. Magnetite, gray, with a metallic nucleus, white. Diameter of spherule, 30 microns. B, spherule from the 
Atlantic Ocean, about 25 cm. below the sediment surface. Same type as A, with imperfect polish. Diameter of 
spherule, about 80 microns. C, spherule from the same sample as A. Magnetite, gray, metallic nucleus, white. 
Diameter, 120 microns. 
220 cm., the numbers were low, rising again 
to somewhat higher values below 220 cm. 
The average number for the whole core was 
130 spherules per kg., whereas between 52 
and 220 cm. it was only 30, compared to the 
average for the uppermost 50 cm. of 500 per 
kg. (Fig. 7). 
To ascribe these very remarkable variations 
in the numbers of the spherules only, or even 
mainly, to changes in the rate of sedimenta- 
tion seems unwarranted. That even in the 
uppermost layers the rate of sedimentation 
was higher than in the central Pacific Ocean 
is indicated by radium measurements in a 
neighbouring short pilot core, Number 133 
B, which contained on an average 11 units 
of the 12th decimal place of Ragr/gr, com- 
pared to from 40 to 50 units in Red Clay from 
the central Pacific. Thus the rate of sedimen- 
tation can be estimated for the upper parts 
of Core 133 at 10 mm. in 1,000 years. 
core 187. This core, raised from a depth 
of 2,500 metres in the eastern Mediterranean 
southwest of Cyprus, was a narrow one and 
had a total length of 9 Vi metres. Hence fairly 
long sections of 30 to 70 cm. had to be used 
for extracting the spherules. The lime content 
was moderately high, varying between 20 and 
40 per cent of CaCC> 3 . The number of spher- 
ules per kg. of lime- and salt-free sediment 
varied considerably along the length of the 
core, from 190 near the surface to an absolute 
maximum of 1,130 in the section 166-235 
cm., declining from there, both upwards and 
downwards, to 5 and 10 per cent respectively 
of the maximum value. 
At another maximum, in section 438-506 
cm., 491 spherules were found per kg. of 
sediment. In the very lowest parts of the core, 
860-950 cm., only 38 and 49 spherules re- 
spectively were found. It must, however, be 
emphasized that where control samples from 
