422 MR. J. DTJKHAM 0I( THE VOLCANIC ROCKS 



consisting entirely of volcanic ash, finely stratified, extend along 

 the beach some five or six hundred yards. These sandstones are 

 much altered, and in some instances overlain by altered andesite, 

 into which the sandstones seem to pass insensibly. In proximity to 

 the felstone the sandstones and andesites are greatly altered, both 

 in texture and colour, the dark grey sandstones and nearly black 

 andesite being changed into a rock almost undistinguishable in hand 

 specimens from the yellow sandstone of the Lower Carboniferous 

 rocks. As the distance from the felstone increases, the rocks, both 

 sedimentary and volcanic, gradually assume their natural colours. 

 Further to the eastward the sandstones gradually lose their cha- 

 racteristic appearance, and seem to pass almost imperceptibly into 

 the altered andesites and basalts until they are entirely replaced 

 by these rocks, which continue along the shore until interrupted 

 by a remarkable gap in the otherwise continuous wall of rock which 

 guards the Eirth. This gap is on the shore of Wormit Bay, from 

 side to side of which no solid rock whatever is met with. Back- 

 ward from the shores of the bay, the hills are replaced by a great 

 series of " kames " and gravel-terraces, which extend through the 

 gap some four or five miles to the south, where the opening joins 

 the flat plain of the valley of the Eden, which is on the Upper 

 Old Eed Sandstone. 



The proximity of these younger beds to the gap in the volcanic 

 rocks suggests as an explanation of it, that the rock underlying the 

 " kames " is probably a continuation of the Upper Old Red of 

 central Fife, let down by faults into its present position. This 

 faulting down of the Upper into the Lower Old Red beds is a 

 familiar phenomenon in the neighbourhood. In Forfarshire and 

 Perthshire, on the other side of the Firth of Tay, several examples 

 occur of isolated patches of the upper series being let down into the 

 lower, while faults along the face of the Braes of Gowrie on the 

 north side of the firth, and on the Fife shore opposite, have thrown 

 the Upper down to a much lower horizon than the volcanic rocks of 

 the Lower Old Eed. Indeed it seems probable that all the Upper 

 Old Eed Sandstone remaining has been preserved by being faulted 

 down relatively to the Lower. 



To the eastward of Wormit Bay, the altered andesites &c. extend 

 along the shore for a short distance, until at a point a little to the 

 west of the Tay Bridge they are interrupted by a fault, which brings 

 down among them a very different class of rocks from any found else- 

 where in this district. About half a mile to the eastward, another 

 fault abruptly terminates this exceedingly interesting series of 

 rocks. 



The fault which forms the eastward boundary of these rocks is 

 just under the farm-house of Scroggieside. To the westward of 

 this fault the andesites and basalts are re]3laced by a conglomerate 

 of weU-rounded volcanic stones, which are waterworn fragments of 

 highly altered andesite. The matrix of this conglomerate is formed 

 of a consolidated sand of the same rock, so that the general aspect 

 of this part of the section is very dark, but here and there angular 



