XXIII. Volcanic Disturbance of the Ironstone Measures in the vicinity of Dalry during the Carboniferous Period

R. Craig
1885 Transactions of the Geological Society of Glasgow  
Introduction.-The purport of this paper is to show the inter mittent character of the volcanic ash which disturbs the mineral field on the south and west of the village of Dairy; and in bringing this subject forward it may add to the interest if I give a passing notice of other volcanic eruptions found in the locality. The Carboniferous strata of North Ayrshire and Benfrewshire rest upon an extensive group of rocks of volcanic origin, consisting of a series of irregular beds of reddish and
more » ... ish ash, porphyrite, felstone, and dolerite. In the parish of Beith they have been bored to the depth of about eighty fathoms without their base being reached. Good sections are to be seen in the hills and in the water-courses outside of the limestone outcrop. Thin bands of carbonaceous matter are found in the series, and in the bores put down two thin layers of impure coal were discovered, from which it may be inferred that some, at least, of the volcanic eruptions have taken place on a land surface. One of these layers of coal, six inches thick, was found about thirty or forty fathoms below the base of the lower limestone, and may therefore be identical with the " Lady Anne coal" of Benfrewshire, which lies thirty fathoms below the lower limestone, and is seen in outcrop in the Gryfe Water above Bridge of Weir. The volcanic ash seen in sec tions in the parishes of Dairy and Kilbirnie appears to have been VOL. VII. Q on June 28, 2015 at West Virginia University http://trngl.lyellcollection.org/ Downloaded from 234 TRANSACTIONS OF THE GEOLOGICAL SOC. OP GLASGOW. re-arranged under water; water-worn stones are present, and the beds have the appearance of a coarse sedimentary deposit. This extensive volcanic deposit entirely fills up the place of the calciferous strata, which proves that, while the Burdiehouse limestone and its associated deposits were being quietly laid down on the east of what is now Scotland, a continued series of volcanic eruptions was going on in the west and filling up the place of these strata with volcanic matter. Ash-beds in the Lower Limestone.-A long time of repose seems to have followed this period of volcanic eruption, and the sub-series of limestone beds has been quietly laid down without interruption. A shallowing of the sea has taken place during the deposition of the two upper bedg, ending in a land surface, followed by an out burst of volcanic activity. A deposit of clayey ash, running from 18 inches in the Pudduff Burn, Kilbirnie, to 8 feet at Hesselhead, Beith, and divided in some places into two beds by a few inches of carbonaceous shale, has been followed by the land sinking into seabottom, and a long period of quietude, during which above 60 feet of limestones and shales have been laid down. This fine deposit of limestone has been interrupted and brought to a close by another outbreak of volcanic activity, accompanied by an out-throw of ash. At one time I was puzzled with this ashbed and the fossils found mixed up with it (Transactions, vol. vi., p. 9). Fossils of true marine character were found associated with those of estuarine character, and Ostracoda representing deep-sea characters were found in association with land plants. In deepen ing a burn at Old Mill, Beith, the ash and the top of the limestone were cut into and a section exposed, and an inspection of this, with a farther examination of the other sections, explained the dif ficulty. In this section it was evident that there were two deposits of ash divided by a period of time long enough to have allowed a forest of Sigillaria and other plants to have grown up, if not also to decay. The whole is explainable as follows :-The first outbreak of ash was accompanied by the upheaval of the sea-bottom into a land surface. Then followed the forest of Sigillaria, the remains of which, in the shape of roots, are found in North Ayrshire, wherever the stratum in which they are imbedded has been pre served. The land then again became submerged, and a thin deposit was formed full of fish remains of estuarine character. This was followed by a second eruption of volcanic ash, forming a on June 28, 2015 at West Virginia University http://trngl.lyellcollection.org/ Downloaded from on June 28, 2015 at West Virginia University http://trngl.lyellcollection.org/ Downloaded from
doi:10.1144/transglas.7.2.233 fatcat:plj2j3otyfeerce74s7da6buv4