XVII. The Occurrence of Iron Ore in Millstone Grit Lava, Ayrshire

Abstract

In 1895 Mr. John Smith (Trans. Geol. Soc., Glasgow, 10, 133, 1895), contributed a paper to this Society, describing a deposit of volcanic ash in Ayrshire, containing bands of ironstone. During the following twenty years there was practically nothing done in the way of further exploration of these deposits until the urgent demand for a supply of ironstone in this country led Mr. G. V. Wilson, of the Geological Survey Office, Edinburgh, to make a careful inspection of this horizon. The volcanic zone referred to lies immediately below the base of the Coal Measures Series, and is now considered to be of Millstone Grit age. The average section of Millstone Grit, as exposed in North Ayrshire, is as follows:— Bauxitic clay, \- - -| - - 3 to 9 feet. Series of lava flows with interbedded sediments, \- - -| - - 70 to 180 ’’ Monkcastle fireclay, \- - -| - 0 to 20 ’’ Sandstone, \- - -| \- - -| 0 to 20 ’’ Sandy fireclays, and blaes with marine fossils, and occasionally thin limestones, \- - -| - - 0 to 20 ’’ The lava flows are often much decomposed and altered by processes similar in many ways to lateritization, whereby their iron contents has been proportionately increased by the abstraction of silica and alumina. This type of alteration is most common near the top of the series, although in a section at Glenburn it can be observed that the basal flow is also affected. The This 250-word extract was created in the absence of an abstract