Vol. 57.] SILUKIAN [?] ROCKS IN FOEFAESHIRE, ETC. 331 



greater, till a fairly thick band of shale is reached, which is followed 

 by chocolate-coloured and dark-grey shale, the latter containing 

 some carbonaceous material. JS'orthward appears the band of pebbly 

 limestone, which was formerly quarried here. A small band of 

 dark shale runs through the quarry, being the highest visible 

 member of the Margie Series in this section. Still farther north 

 the limestone is repeated by folding, with a persistent dip to the 

 north-west ; but the strata are there inverted, for the shale- 

 bands reappear, though in reverse order. Here the third part of 

 this interesting section ends, for the shales are in conjunction with 

 the slates of the Highland Series. 



The many excellent sections north-east of the North Esk add 

 little to our knowledge of the succession of these rocks. Moreover, 

 with one notable exception, no fossils have been found in them, 

 and it therefore became necessary to determine accurately their 

 lithological characters, a summary of which is now given. 



The Margie Series. 



A characteristic feature of the whole group is the presence, often 

 in considerable quantity, of white and brown clastic mica. AVhere 

 the grits are much crushed there is some difficulty in recognizing 

 them. The occurrence of these micas is, however, of importance, 

 as they serve to distinguish the cleaved Margie Shale from the 

 Highland Slate, in which, so far as this district is concerned, no 

 such micas have been detected. 



The pebbles in the grits consist of quartz and felspar, 

 the former predominating. The felspar-pebbles consist almost 

 entirely of oligoclase ; this, where the rock is not decomposed, 

 possesses the remarkable freshness that is known to characterize the 

 oligoclase of the metamorphic series. This felspar abounds in the 

 adjacent Highland rocks, and probably has been derived from them. 

 The quartz-pebbles may have been obtained from the quartz-segre- 

 gations 80 abundant in the Highland Schists. 



As already indicated, the green conglomerate at the base of 

 the Margie Series is composed of the detritus of the green igneous 

 rock (Jasper and Green-E,ock Series) and contains abundant pebbles, 

 indeed, in places, boulders of that rock. Fragments of jasper are 

 met with in the outcrop in the North Esk, but not in the exposure 

 in the Kirkton Burn, about a mile to the north-east. Some of the 

 larger boulders so closely resemble the basic lamprophyres met 

 with in the Highlands that it was supposed they might be. derived 

 from that source ; but more recent investigation has shown that a 

 similar rock occurs among the Green Kocks, though this special 

 type is not known in the North Esk district. The origin and local 

 character of the green conglomerate is obvious, and attention has 

 been drawn to the probable local origin of the pebbles in the grits. 

 The carbonate-cement in the grits is probably also- of local origin, 

 for it may have been derived from the lime and iron set free by the 

 decomposition of the basic igneous rocks (the Green Rocks). 



Q. J. G. S. No. 227. 2 l 



