86 



THE DEPOSITS OF THE SEA-BOTTOM. 



obliquelv upwards to the right , when the Coeeolith is seen from the upper side, to the left, when it 

 is seen from the under side; in the former case the branches are somewhat spirally twisted to the 

 left, in the latter case to the right If we now turn the table with the preparation we shall, when 

 the Coeeolith is seen from the upper side, observe the following alterations in the cross, when the 

 turning takes place to the left. 



It will be seen that the branches of the cross continue to be spirally twisted to the same side, 

 but alter their mutual position and thickness. When the turning has grown to somewhat more than 

 20 r , we get the position £, where the branches of the cross are almost at a right angle and in the 

 direction of the axes of the Coeeolith, the short branch being still much thicker than the other one. 

 In the next position, at c, where the turning has reached 45 , the thin branch still almost covers the 

 major axis, while the thick branch has got an oblique direction, contrary to the first position. If the 



turning is continued still 20 , to d, both branches will be of equal thickness, and be situated almost 

 symmetrically to the major axis; the hitherto thicker branch will be the one most spirally twisted. 

 Finally, when the Coeeolith has got to the horizontal position (r) the hitherto thinner branch has be- 

 come thick and transverse, we have exactly the same figure as that of the starting point, and by a 

 further turning we shall get the same series of figures, in all four times for each whole turning. If 

 the Coeeolith is seen from the inner side, we may, by a turning to the right, get the same figures in 

 positions symmetrical to those of the preceding ones. 



To understand how these phenomena arise, we must suppose the central ring to be built of 

 threads of calcite or another modification of calcium carbonate, chiefly situated in radiating directions, 

 but arranged, however, in a rather peculiar way. In each of the positions drawn in the preceding 

 figure, the threads of calcite must be parallel to the direction of the thread-cross in the places where 

 the black cross is situated. If we now draw the middle lines of the branches of the cross in the 

 four positions on a joint figure, and indicate the directions that the threads of calcite are to have 



