730 GRIFFIN AND GOLDBEBG [CHAP. 26 



integrated peak areas of the minerals was used. This tends to compensate for 

 fluctuations in orientation and to a certain degree the effect of variations in the 

 crystalhnity. Compensation for the effects of isomorphous substitution in both 

 the ilhte and chlorite groups of minerals is difficult to make. Most probably this 

 effect will be slight for clay minerals from the marine environment where the 

 major cation concentrations in the water are nearly constant. 



To give equal weight to illite when comparing it to montmorillonite (i.e. the 

 Mil ratio), the 10 A peak area was multiplied by 4. This compensates for the 

 diff'erence in the form factor of the two minerals (Bradley, 1945a; Johns, Grim 

 and Bradley, 1954). 



3. Surface Distribution of Clay Minerals 



The clay-mineral distribution in the upper few centimeters of cores taken 

 from the Pacific is shown in Figs. 1, 2, 3 and 4. A most dramatic observation 

 is the systematic distributional trends in the North Pacific, whereas there 

 appears to be no obvious pattern in the South Pacific. The equatorial region 

 acts as a natural boundary between these two provinces of clay-mineral dis- 

 tribution. The following generahzations are derived from our experimental 

 data, partly shown in the plots. 



A. North Pacific 



1. Abundant illite was found in all samples, whereas montmorillonite, 

 chlorite and kaohnite were generally present and their abundances are a function 

 of location. 



2. Montmorillonite was generally more abundant in nearshore sediments. 

 The montmorillonite/illite ratio {Mjl ) is > 1 along the coast of North America 

 and Asia; however, the ratio decreases in high latitudes (Fig. 1). Above 50°N 

 the coastal sediment ratio generally has a value < 1. Between the coastal area 

 and the mid-ocean areas of the eastern Pacific there is a band of sediment 

 which has Mjl ratios varying between 0.5 and 1.0. This band is not defined 

 off the Asiatic coast. In the mid-oceanic areas, the ratio is generally quite low 

 and has values lying between and 0.5. 



3. Chlorite abundance, based on the presence of the 14 and 4.7 A peaks, 

 increased with increasing latitude in nearshore sediments (Fig. 2). However, 

 the relatively high abundances in coastal sediments off Northern Canada, 

 Alaska and the Aleutian Islands decrease with increasing distance from land. 



4. Kaolinite abundance, which was based on the presence of the 7.1 and 3.5 A 

 peaks and the absence of the 14 and 4.7 A peaks, was confined to nearshore 

 areas on both the east and west coasts. However, with increasing distance from 

 land, it is difficult to evaluate the kaolinite abundances because the 14 and 4.7 A 

 chlorite peaks begin to appear in the diff"raction tracings. 



5. The 7.1/10 A peak-area ratios (chlorite -f-kaolinite)/(illite) show a cor- 

 respondence to the Mjl ratio (Fig. 3). The ratio is usually < 1 along the eastern 



