732 J. W. JTJDD ON THE SECOND AET ROCKS OF SCOTLAND. 



The Upper Greensand itself appears to consist of two portions, the 

 higher calcareous, the lower arenaceous. The calcareous beds 

 derive their character from being almost wholly made up of shells of 

 Exogyra conica, and are in fact great oyster-banks. Both the cal- 

 careous and the arenaceous beds contain the characteristic grains 

 of glauconite. 



The Upper Greensand behind Carsaig House is found to rest di- 

 rectly upon the sandy strata of the Middle Lias (Scarpa Series). 

 When traced westwards, however, the Greensand is found occupying 

 gradually lower levels, owing to a dip in that direction, till at last it 

 reaches the sea-level at a point beyond the celebrated Nun's Cave. 

 Throughout the whole of its exposure on this coast the strata are 

 crowded with Ex ogy rce and other shells ; but the beds of highly cal- 

 careous character appear to be somewhat local, and do not seem to 

 occur at the westernmost exposures of the formation. 



The next place at which the Upper-Greensand strata are 

 exposed is about Loch Aline. Here the beds in question are found 

 overlapping the Lower-Lias strata, and can be well studied on the 

 shore along the western shores of the Loch, at a little distance above 

 the inn and village. None of the strata are here so highly calca- 

 reous as above Carsaig House ; but beds of dark green clayey sand 

 occur at several points in the series. The fossils are abundant and 

 of the same species as at Carsaig. 



The Upper-Greensand strata presenting everywhere the same cha- 

 racters, but apparently diminishing in thickness as we go north- 

 wards, can be detected around the head of Loch Aline, about Loch 

 Arienas, and, finally, in the remarkable outliers of Morvern, where 

 the most northerly exposures of the beds of this age occur. 



At Gribun on the shores of Loch-na-Kael and in the opposite 

 islet of Inch Kenneth, the Upper Greensand makes its appearance and 

 presents somewhat different features from those which characterize 

 it at the localities already described. The strata there are found 

 resting directly upon the Poikilitic beds already noticed, and, in- 

 deed, are largely formed of the materials derived from those beds. 

 Under these circumstances it is not surprising that the line of 

 division between the Cretaceous above and the Poikilitic below is 

 often very obscure. While the upper part of the Greensand here 

 consists of the ordinary glauconitic sands, in which I have detected 

 the common Exogyra conica, species of S&rpulce, and Sjwngia para- 

 cloxa, the lower part consists of a conglomerate of quartzite pebbles 

 derived directly or indirectly from the old gneissic rocks of the 

 district, upon which the Poikilitic strata here rest. There are 

 grounds, indeed, for believing that the Upper-Greensand strata here 

 completely overlap the Poikilitic beds, and rest directly upon the 

 old gneiss rocks themselves. At two or three points at Gribun the 

 peculiar beds of the Scottish Chalk — here converted into a siliceous 

 material — are seen crushed out from beneath the overwhelming 

 masses of basaltic lava that cover all the Secondary strata to such a 

 great depth at this place. The accompanying section (fig. 11, p. 731) 

 illustrates the general relations of the beds seen at Gribun. 



