452 PRINCIPLES OF STRATIGRAPHY 



meters. The 118 samples obtained by the Challenger expedition 

 were distributed as follows : 



Less than 1,000 fathoms (1,830 m.) 



Between 1,000 and 1,500 fathoms (1,830-2,750 m.) 



Between 1,500 and 2,000 fathoms (2,750-3,660 m.) 



Between 2,000 and 2,500 fathoms (3,660-4,570 m.) 



Below 2,500 fathoms (4,570 m.) 



118 



It will be observed that the percentage of CaCOs in the oozes 

 decreases with depth, being only 50% in the samples from the 

 greater depths. The average of the 118 samples gave 64.5% of 

 CaCOg, 30.6% of non-calcareons silt, 3.3% mineral particles, and 

 1.6% siliceous organisms. The lime was distributed as follows: 



Remains of pelagic organisms 53 • i % 



Remains of benthonic organisms 2.1% 



Remains of other organisms 9 . 3% 



64-5% 



Among the mineral matter other than lime associated with the 

 Globigerina oozes may be mentioned glauconite, and phosphate and 

 manganese concretions. 



Sir John Murray conckided from experiments made that it takes 

 the dead foraminiferal shells from three to six days to sink to a 

 depth of 4,500 meters, the rate being slowest in the deeper water. 

 Solution of the lime of the shells by the sea water increases rapidly 

 with depth, owing to the increase in pressure. Thoulet found that 

 the rate varied greatly with the size of the shells and particles, 

 those averaging 0.75 mm. in diameter taking 1.09 days to reach a 

 depth of 4,500 meters, while those having a diameter of only 0.12 

 mm. required 7.47 days for the same distance. 



Not infrequently fragments and blocks of terrestrial rocks are 

 found in the Globigerina deposits, as, for example, fossiliferous 

 Palaeozoic rocks marked by glacial scratches, and found by the 

 French expedition northeast of the Azores, 1,100 km. from the Euro- 

 pean coast, carried there by drift ice probably during the last glacial 

 period ; and the coarse fragments of crystalline rock found in the 

 South Atlantic between Tristan da Cunha and Kapstadt, in 35° to 

 36° S. lat., and others from the Indian Ocean. 



The areal distribution of the Globigerina ooze is a considerable 



