chap. xiv. Section of the Uspallata Range. 521 



at an angle from 70° to 80° : in one instance, the clay- 

 slate dipped not only at a different angle, but to a 

 different point from the overlying formation. In these 

 cases the two formations certainly appeared quite un- 

 conformable : moreover, I found in the clay-slate one 

 great, vertical, dike-like fissure, filled up with an in- 

 durated whitish tuff, quite similar to some of the upper 

 beds presently to be described ; and this shows that the 

 clay-slate must have been consolidated and dislocated 

 before their deposition. On the other hand, the strati- 

 fication of the slate and grauwacke, 1 in some cases gra- 

 dually and entirely disappeared in approaching the 

 overlying white conglomerate; in other cases the 

 stratification of the two formations became strictly con- 

 formable; and again in other cases, there was some 

 tolerably well characterised clay-slate lying above the 

 conglomerate. The most probable conclusion appears 

 to be, that after the clay-slate formation had been dis- 

 located and tilted, but whilst under the sea, a fresh and 

 more recent deposition of clay-slate took place, on which 

 the white conglomerate was conformably deposited, with 

 here and there a thin intercalated bed of clay-slate. On 

 this view the white conglomerates and the presently to 

 be described tuffs and lavas are really, unconformable 

 to the main part of the clay-slate ; and this, as we have 

 seen, certainly is the case with the clay-stone lavas in 

 the valley of Oanota, at the western and opposite base 

 of the range. 



Thirdly : on the white conglomerate, strata several 



1 The coarse, mechanical structure of many grauwackes has always 

 appeared to me a difficulty ; for the texture of the associated clay- 

 slate and the nature of the embedded organic remains where present, 

 indicate that the whole has been a deep-water deposit. Whence have 

 the sometimes included angular fragments of clay-slate, and the 

 rounded masses of quartz and other rocks, been derived ? Many 

 deep-water limestones, it is well known, have been brecciated, and 

 then firmly recemented. 



