1867.] 



MACKINTOSH — CUR VATXTRE OF SLATY LAMINA. 



323 



sections exposed on the sonth flank of the Himalayas, and suggests 

 a parallelism between them and those exhibited in the Alps. The 

 clays, sands, and conglomerates of the Sivaliks are very like those of 

 the Molasse ; and in both regions the coarser deposits prevail 

 towards the top. In the Himalayas also the younger Tertiary de- 

 posits almost invariably dip towards the mountain-range which they 

 fringe, — the plane of contact inclining in the same direction, and 

 thus producing actual, though not parallel, superposition of the older 

 rocks. All the arguments which have been used to prove pro- 

 digious faulting in the case of the Alps would therefore, the author 

 states, be quite as applicable to that of the Himalayas. But, as 

 regards the latter range, Mr. Medlicott brings forward evidence 

 which appears to him .sufficient to prove that the present contact 

 of the Sivalik formation with the mountains is the original one, 

 modified only by pressure, without relative vertical displacement ; 

 and that the sinking of the mountain-mass is the proximate cause 

 of the contortions of the Tertiary strata. He then endeavours to 

 show that this explanation is equally applicable to the Alps, espe- 

 cially as it seems also to account for collateral phenomena which 

 appear difficult of explanation consistently with the ordinary hypo- 

 thesis ; and he concludes by discussing the current theories of the 

 formation of lake-basins, in relation to the more immediate subject 

 of his paper. 



2. On some striking Instances o/ ^A^ Terminal Curvature of Slaty 

 Lamina in "West Somerset. By D. Mackintosh, Esq., F.G.S. 



Contents, 



1. Introduction, 



2. Sections in a Quarry nearWivelis- 



combe. 



3. Terminal Curvature of Laminaa 



near Kaleigh's Cross, 



4. Transportation of Blocks, 



5. Apparent Reversal of Dip near 



Gup worthy. 



6. Concluding Eemarks, 



1. Introduction. — During the last two years I have been making a 

 series of observations in the West of England and in Wales, with the 

 hope of being able to throw some fresh light on the relative nature 

 and extent of oceanic and atmospheric denudation, and on the origin 

 of superficial accumulations. In some parts of Siluria, during the 

 spring of last year, I supposed I had met with a proof of tranquil 

 marine deposition in horizontally arranged chips of slate resting on 

 the edges of highly inclined laminae, until I found that I had been 

 looking on a continuation of these edges in a curved-back position, 

 instead of seeing the curvature in profile. 



In the autumn of 1866 I noticed several instances of the above 

 phenomenon, which have not yet been described by geologists *. On 

 the nearly level floor of one of the valleys which indent the southern 

 slope of the eastern part of the Quantock range of hills, I found the 



* For an instance near Ashburton, noticed by Mr, Godwin-Austen, see Trans. 

 Geol. Soc. 2nd series, part ii. vol. vi. p. 437. 



