. The Quarterly journal of the Geological Society of London. axis. Itcontains boulders similar to those that have been enumeratedabove, but more sporadically distributed. The main Grarvellach dolomite, which yields so many fragmentsto the Portaskaig Conglomerate in its vicinity, recalls in appear-ance the dolomite intercalations of the conglomeratic series inIslay, only it is thicker and purer. It is impossible, withoutboring, to decide whether the Garvellach dolomite is similarlyinterstratified, or whether it completely underlies the conglomeraticsequence. The interstratified dolomites in Isl
. The Quarterly journal of the Geological Society of London. axis. Itcontains boulders similar to those that have been enumeratedabove, but more sporadically distributed. The main Grarvellach dolomite, which yields so many fragmentsto the Portaskaig Conglomerate in its vicinity, recalls in appear-ance the dolomite intercalations of the conglomeratic series inIslay, only it is thicker and purer. It is impossible, withoutboring, to decide whether the Garvellach dolomite is similarlyinterstratified, or whether it completely underlies the conglomeraticsequence. The interstratified dolomites in Islay, it will be remem-bered, have suffered from contemporaneous erosion, and thereforethe erosion effects in connexion with the Grarvellach bed are inkeeping with either alternative. (3e) Islay Quartzite. North Islay.—The Islay Quartzite is not wholly representedin North Islay, as the top is wanting. In spite of this, NorthIslay is the most interesting portion of the archipelago from ourpoint of view, for it enables us to realize the anticlinal nature of. [Anticline of dolomite, rising to 150 feet, enveloped in Portaskaig Conglo-merate. The cliff faces south-westwards. Sketched from a photographby E, Limn, 10, pi. iv, p. 32.] part 2] THE I SLAY ANTICLINE. 147 the Central Islay Fold. The following suhclivisions are recognizedin the Quartzite Series, in descending order : — Pebbly Quartzite. Upper Fine-Grained Quartzite. Dolomitic Group ( Pucoid Beds of the Geological Survey Memoir),with often a massive quartzite intercalation ( Pipe Rock of theMemoir) near the base. Lower Pine-Grained Quartzite. In regard to the two lower subdivisions and their relations tothe Portaskaig Conglomerate, the above is in agreement withthe succession as stated by Mr. Wilkinson. But, whereas hebelieves that the Dolomitic Group is the highest stratigraphicaldivision preserved in the island, I propose to show that it is over-lain by much the greater portion of the Islay Quartzite. The structure and s
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Keywords: ., bookcentury1800, bookdecade1840, bookidquarte, booksubjectgeology
