GEOLOGY OF THE SHALES 589 



oolites varie's in the different colored phases, but they are iiiiiformh^ dis- 

 tributed within each phase. 



The structural features of the beds are interesting. Evidences of cross- 

 bedding are rare, and "here and there a conglomerate, varying in com- 

 position from pebbles of various kinds of rocks to pieces of bone and 

 teeth of reptiles and amphibians, occurs among the other rocks." All 

 tlie beds show rapid lateral variation in composition, as well as in color, 

 and a given bed may change in this way within a few feet. Nodules of 

 calcite which are 8 to 10 inches in diameter occur locally. A remarkable 

 feature of the beds is the nodular form the material assumes on weather- 

 ing. Many of these iiodules are 12 to 14 inches in diameter and most 

 of them are well rounded (figure 1). In the upper massive layer this 

 nodular strncture is especially well developed. 



Description of the Oolites 



general state 31 en t 



The material which the writer collected for study represents principally 

 the red, yellow, and green phases of the formation. Oolites occur in other 

 colored shales, but the above are taken as being typical of the oolitic 

 phases. Whatever the color of the rock, the oolites are white. Only one 

 exception to this was observed, the interior of an oolite being pink and 

 tlie remainder white. 



THE OOLITES IN THE RED SHALE 



This shale is a dark purplish I'ed in color, and the oolites in it comprise 

 more than 50 per cent of the rock. The shale is sandy. The grains are 

 very small and not readily recognizable, although they may be seen 

 through a binocular with a magnification of twenty-five. The oolites 

 sliow^ a tendency to aggregate into groups of from 6 to 25 in number. 

 Tliey are rarely near enough to touch one another in these aggregates, 

 but are merely more numerous there tlian elsewhere (figure 2). Tliey 

 are not related iji position to any structural features of the rock. 



Under the microscope tlie sand is seen to be uniformly disseminated 

 throughout tlie shale and the oolites (plate 21, figures 1-3). It consists 

 of angular quartz grains, wliieli are rarely over .1 millimeter in diameter, 

 the majority being less than ,05 millimeter. 



The oolites occur in two distinct sizes. The larger ones average about 

 .05 millimeter in diameter, ranging from .5 to .7 millimeter. This con- 

 stant uiuform size of about .(55 millimeter should be noted. The smaller 



XLIV— Bull. Gkol. Soc. Am., Vol. 2n, 1017 



