GYP6UM. 47 



The broken and disturbed character of the series renders it difficult 

 to fix the place of these alum shales with certainty or narrowly, but 

 they probably form a band not far above the lowest layers of the 

 gypsum. In the country lying southward and south-eastward of this 

 district two zones of alum shales occur, one near the base of the nummu- 

 litic rocks, the other in the Jurassic series ; these here may be the repre- 

 sentatives of the newest of those in the nummulitic rocks, for though 

 the associated beds differ, the relative place beneath the mass of the 

 nummulitic limestone is approximately the same. 



Stratification. — The stratification of the gypsum is not uniformly 

 evident ; in some places the beds appear to be thick and massive, or the 

 bedding laminae are indistinct ; in others it becomes thinly divided or 

 flaggy, showing alternations of gray and whiter colour. The lamination 

 is rarely parallel ; more frequently it assumes complex folds, sometimes 

 on as small a scale as may be observed in the contorted foliation of 

 gneiss or other crystalline rock. The alternation of the gypsum with 

 the gray clays is in places very distinct, in others most obscure, and 

 towards the top of the main gypseous band, this frequently passes by 

 alternation of thin layers into the red clay zone which follows. Where 

 the soft clay has been washed from between these upper gypsum layers, 

 as well as occasionally in other parts where the stratification is clear, 

 distinct current or ' ripple' marks have been observed on the surfaces 

 of the beds, indicating their having been accumulated in shallow water. 



Fossils. — No organisms whatever have been found in the gypsum, 

 and none in the associated gray clays, except the obscure grass-like 

 fragments already mentioned, but in a limestone band near the top of 

 the gypseous group associated with gray clays, some small and fragment- 

 ary shell impressions were detected. One seemed to be a fragment of an 

 oyster, the others might have been anything. 



Wasting. — The solubility of the gypsum by rain is plainly shown 

 by the way in which its surface is frequently deeply fretted into minia- 



( 151 ) 



