Yol. 57.] SILURIAN [?] EOCKS IX FORFAESHIKE, ETC. 329* 



Conglomerate for about a mile, and thereafter the Lintrathen 

 porphyrite. Immediately to the north of the latter igneous mass 

 the rocks now to be described appear. The section is divisible iuto 

 three parts. 



The first and southernmost — about 400 yards long — is best seen 

 when the river is low. The strata consist of sandstones or grits, 

 reddish or pale brown on a weathered surface, but almost white 

 in fresh fracture. Their milky-white aspect is due to the matrix 

 being composed of carbonate of iron and lime, which effervesces 

 briskly with acid. The pebbles in these grits may be seen by 

 the eye, though at this locality they are rarely as big as peas. 

 Some thin bands of white, grey, and chocolate-coloured shales 

 are associated with these grits, which are sometimes cleaved. The 

 characteristic feature of these shales, however, is the occurrence 

 in them of original clastic micas, which serves to distinguish them 

 from the Highland slates with which they were formerly grouped. 

 Both shales and grits are seen to lie at all angles in the bed of 

 the river, sometimes nearly vertical, sometimes almost horizontal. 

 Local lines of shear or crush are frequenth* met with. jSTever- 

 theless a close examination of the section leads to the belief that 

 the actual thickness of the strata is small. 



At the northern end of this part of the section are two dykes 

 of dolerite, probably of Tertiary age, and on the north side of the 

 second dyke the curious pebbly limestone (Margie Limestone) was 

 formerly noted by Lieut.-Col. Imrie. It is no longer visible, being 

 now covered by river-gravel. 



Prom the foregoing description it appears that the first part of 

 the J^Torth Esk section exposes the members of the Margie Series, 

 consisting of grits, shales, and a little band of pebbly limestone. 



The second part of the Xorth Esk section begins on the north 

 side of the second dolerite-dyke just referred to, where a wall- 

 like mass of rock crosses the river (see fig. 1, p. 330). The latter 

 consists of a confused mass of jasper, calc-jasper, and Green Rock, 

 which has obviously been subjected to intense dynamic action. 

 The wall-like mass is followed by much deformed Green Rock, 

 becoming more massive farther north, which, on examination, is 

 found to be a crushed and decomposed basic igneous rock. North- 

 ward some thin bands of brittle red jasper are infolded with the 

 igneous rock, and still farther up stream there is a considerable 

 mass of jasper. On the sides of the rocky gorge the observer may 

 note that the rocks are isoclinally folded, the limbs of the folds 

 being nearly vertical ; and it may further be seen that the increased 

 thickness of the jasper is mainly due to repetition by folding. 

 Moreover, the mode of occurrence of the jasper in the folds of the 

 Green Rock shows that it is stratigraphicaily above that rock. 

 Northward, some phyllite occurs, which, from the e\idence in the 

 gorge, is stratigraphically above the jasper. At the bend of the 

 river, at the northern end of the Wood of the Burn, some interesting 

 rocks appear, which will be described in the forthcoming Geological 



