Ch. Y.J 



INCLINED STKATIFICATION. 



47 



Fir. 61. 



water to marine deposits, afterwards to be described. It will also appear, 

 in the sequel, how much light the doctrine of a continued subsidence of 

 land may throw on the manner in which a series of strata, formed in 

 shallow water, may have accumulated to a great thickness. The exca- 

 vation of valleys also, and other effects of denudation, of which I shall 

 presently treat, can alone be understood when we duly appreciate the 

 proofs, now on record, of the prolonged rising and sinking of land, 

 throughout wide areas. 



To conclude this subject, I may remind the reader, that were we to 

 embrace the doctrine which ascribes the elevated position of marine 

 formations, and the depression of certain freshwater strata, to oscillations 

 in the level of the waters instead of the land, we should be compelled to 

 admit that the ocean has been sometimes everywhere much shallower 

 than at present, and at others more than three miles deeper. 



Inclined stratification. — The most unequivocal evidence of a change 

 in the original position of strata is afforded by their standing up perpen- 

 dicularly on their edges, which is by no means a rare phenomenon, es- 

 pecially in mountainous countries. Thus we find in Scotland, on the 

 southern skirts of the Grampian's, beds of pudding-stone alternating 

 with thin layers of fine sand, all placed vertically to the horizon. When 

 Saussure first observed certain conglomer- 

 ates in a similar position in the Swiss Alps, 

 he remarked that the pebbles, being for the 

 most part of an oval shape, had their 

 longer axes parallel to the planes of strati- 

 fication (see fig. 61). From this he in- 

 ferred, that such strata must, at first, have 

 been horizontal, each oval pebble having 

 originally settled at the bottom of the 

 water, with its flatter side parallel to the horizon, for the same reason 

 that an egg will not stand on either end if unsupported. Some few, in- 

 deed, of the rounded stones in a conglomerate occasionally afford an 

 exception to the above rule, for the same reason that we see on a shingle 

 beach some oval or flat-sided pebbles resting on their ends or edges ; 

 these having been forced along the bottom and against each other by a 

 wave or current so as to settle in this position. 



Vertical strata, when they can be traced continuously upwards or 

 downwards for some depth, are almost invariably seen to be parts of 

 great curves, which may have a diameter of a few yards, or of several 

 miles. I shall first describe two curves of considerable regularity, which 

 occur in Forfarshire, extending over a country twenty miles in breadth, 

 from the foot of the Grampians to the sea near Arbroath. 



The mass of strata here shown may be nearly 2000 feet in thickness, 

 consisting of red and white sandstone, and various colored shales, the 

 beds being distinguishable into four principal groups, namely, No. l,red 

 marl or shale ; No. 2, red sandstone, used for building ; No. 3, conglom- 

 erate ; and No. 4, gray paving-stone, and tile-stone, with green and red- 



Vertical conglomerate and sandstone, 



