84 MALLET^ VINDHYAN SERIES. 



The Sirboo shales which rest directly on the lower sandstone are 



well exposed on the flanks of Sirboo hill. The following section was 



taken at the south-west angle : — 



Ft. In. 



Gently inclined ground at base of hill, shales not seen ... 80 



Thin, regularly- bedded, greenisli, aluminous shale, brittle and 



splintery ... ... ... ... ... 26 



Similar shale with bands of sandstone from f to 1 inch thick ... 26 

 Greenish, aluminous shale, thicker bedded, some few beds as 

 much as 4 or 5 inches : grey in some parts : much broken 



up where exposed : a few sandy layers ... ... 44 



Greenish hard silicious flags more or less broken ... ... 60 



Alternate silicious and aluminous shale ... ..." ... 17 



Aluminous shale with arenaceous layers from J to 4 and 6 inches 26 



Similar shales without arenaceous layers, some beds greyish ... 320 



Obscured by talus ; seems nearly all shale ... ... 165 



Sirboo shales (a few beds at bottom not included) ... ... 764 



Upper Bundair sandstone, to top of hill ... .,, ... 137 



901 



The outlying hill at Ponri (450 feet high,) south of Myhere, 

 exposes similar thin-bedded aluminous shale, slightly micaceous with 

 occasional bands of sandstone J to 4 inches thick ; chiefly greenish with 

 some dark grey bands. The general aspect of these beds is everywhere 

 very much the same wherever they are seen ; in the Bundair scarp 

 (see Plate 3) or in the outlying hills to east. When unprotected by sand- 

 stone talus, as on the hill at Ponri, they weather into very steep 

 precipitous faces. 



At Sirboo hill the thickness of the Sirboo shales is about 750 feet, 

 but this amount is somewhat reduced at Myhere, where the lower Bun- 

 dairs altogether have a thickness of about 1,300 feet. In following 

 them up the Tonse valley the lower members seem to diminish some- 

 what, but expand again to the westward. 



( 84 ) 



