On the Occurrence of the Genus Girvanella in Oolitic Rocks, and Remarks in Oolitic Structure

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Abstract
In January 1888 I commenced a systematic examination of the oolitic rocks in the Carboniferous and Jurassic series. The subject was, of course, by no means new, but I was under the impression that there had been no systematic investigation of the structure of those rocks, though many authors had referred to the subject. My attention was subsequently called to Dr. Sorby's illustrated appendix to his Presidential Address to this Society, 1879, and I found that much of the work I contemplated was already done. I had, however, at an early stage of the work, discovered that the little-known genus Girvanella was of frequent occurrence in oolitic rocks, which appears to have escaped the notice of Dr. Sorby. My work then resolved itself into a search for that organism; but, as I had to make over 230 thin slides for microscopic examination, I have been able to work out the structure of the rocks in greater detail than Dr. Sorby has done, and I trust that an account of the observations deduced from those slides may prove a worthy supplement to his work. The Genus Girvanella , Nich, & Etheridge, jun . This apparently insignificant organism was first noticed by Prof. H. Alleyne Nicholson and Mr. Robert Etheridge, jun., in their ‘ Monograph of the Silurian Fossils of the Girvan District in Ayrshire’ (Part I., 1878), and was described as consisting of “Microscopic tubuli with arenaceous or calcareous (?) walls, flexuous or contorted, circular in section, forming loosely compacted masses. The tubes apparently

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