18 medlicott^ shillong plateau. 



5. The Cretaceous Seeies. 

 It would scarcely be possible to make anytbing like an exact 

 litbologico-stratigrapbical scale of tbe cretaceous deposits at Cherra Punji. 

 SmaU as is tbe lengtb of tbe section and considerable as is tbe total 

 tbicknesSj tbere is no cbaracter constant in, or to, any one borizon. Tbe 

 series may be said to be sandy tbrougbout ; but tbe varieties are very 

 numerous, and tbeir distribution is most inconstant. Tbe nature of 

 tbese deposits and tbeir unassorted condition would seem to be owing 

 to tbe proximity of tbe area of erosion from wbicb tbey were derived. 

 Tbe tbiekness cbanges from 1,200 feet at tbe scarp of tbe plateau to 

 670 feet under tbe middle of tbe station of Cberra; at about one mile 

 furtber nortb, it is reduced to 560 ; at a point ten miles from tbe scarp, 

 wbere tbe nummulitic beds make tbeir last appearance, tbere is only 

 about 100 feet of cretaceous sandstone. Tbis very rapid reduction is an 

 original feature, in no way. aided by denudation. Still we are far from 

 baving ascertained tbe limit of extension of tbe formation : for many 

 miles to tbe nortb outlying patcbes of tbe cretaceous sandstone are found ; 

 not indeed as capping to tbe bigb points, but ratber on tbe sides of 

 existing depressions ; sbowing tbat tbe pre-cretaeeous surface of tbe meta- 

 morpbie area bad to some extent tbe same contour as tbe present one. 

 Beneatb tbe strata of tbe main area tbe surface of tbe metamorpbie 

 rocks seems remarkably even. 



Tbe difficulty tbat bas been felt in assigning a borizon of separation 

 between tbe nummulitic and cretaceous deposits at Cberra Punji is 

 attributable to tbeir general similarity of composition and of arrange- 

 ment, and to tbe fact tbat between tbe two known fossiUiferous rocks 

 in eacb tbere is a band of some 300 feet tbiekness, in wbicb no fossils 

 bave been found save vague stem-like non-carbonaceous vegetable im- 

 pressions, and wbicb migbt belong to eitber formation. Tbere is indeed 

 a superficial feature wbicb markedly suggests tbe association of tbis 

 band witb tbe lower series : tbis is tbe rock wbicb so generally forms a 

 ( 168 ) . 



