TRANSACTIONS OF SECTION C. 863 



body averages about -012 of an iuch in diameter, but, small as it is, the calcareous 

 sphere has been an important contributor to the buildinj,^ of the rocks. 



As calcisphfera is confined to the Carboniferous Limestone, and is so numerous 

 that it is seldom a thin section of the rock is obtained without finding it, the 

 organism is useful in determining the strata when doubtful. So far, the author 

 has not found calcisphsera in the Lower Limestones, and the same remark applies 

 to foraminifera. 



Above the horizon of the Gully Oolite the lower beds of the Middle Limestone 

 are characterised by the occurrence of the curious organism Mitcheldeania, but it 

 is not confined to this horizon. 



Next follow limestones and calcareous shales full of the remains of little- 

 understood forms of microscopic life, which must have existed in great profusion. 



As before remarked, the Middle Limestones are characterised by foraminifera 

 and calcisphsera. At first these occur sparingly, but, later on, the rock is little 

 more than a Carboniferous foraminiferous ooze. Remains of corals occur and 

 other well-known fossils, but the bulk of the 1,600 feet of limestone included in 

 the Middle Series is in the main a vast calcareous deposit of the remains of 

 microscopic life which lived in the Carboniferous waters. 



Owing to the Upper Limestones being so built over, the author is at present not 

 in a position to describe the microscopic life which the strata probably contain 

 associated with large organisms. • 



3. On the Revision of South Wales and Monmouthshire hy the 

 Geological Survey. By A. Strahan. 



[Communicated by permission of the Director-General.] 



The original geological survey of South Wales was made under the direction 

 of Sir Henry De la Beche. The exact date of its commencement is uncertain, but 

 I am informed by Mr. Aveline that in 1840, when he joined, the staff was engaged 

 in the neighbourhood of Cardifl:', and in 1841 Ramsay on his appointment found 

 that the survey had progressed westwards into Pembrokeshire and was at work at 

 Tenby and St. David's.^ By the end of 1845 the maps had all been published, 

 A complete list of the names which appear on them consists of H. T. De la Beche' 

 J. Phillips, D. H. Williams, A. C. Ramsay, W. T. Aveline, J. Rees, T. E. James' 

 W. E. Logan, H. \V. Bristow,^ and H. B. Woodward.^ ' 



Previously, however, to the entry of the Survey into South Wales a considerable 

 tract had been mapped by Sir W. E. Logan. ' Unaided he commenced, in 1 831 a 

 geological survey of part of the great South Welsh Coal-field, extending from 

 Crown (Cwm) Avon to Carmarthen Bay, and completed it in seven years, at no 

 small pecuniary sacrifice. Such was the estimate of the accuracy and value of this 

 survey by the late Director of the Geological Survey of Great Britain, Sir Henry De 

 la Beche, that with Sir William's consent it was adopted as part of the national 

 work/ 3 At the meeting of the British Association in Liverpool in 1837 Logan 

 exhibited his work, and in 1842 it was referred to by De la Beche as a beautifully 

 executed map.^ After the lapse of nearly fifty years these maps, admirable though 

 they were, considering their date and the circumstances under which they were 

 made, had become obsolete. Not only was the topography scarcely recognisable, 

 but the development of the steam-coal trade had led to the opening out of'many of 

 the Monmouthshire and Glamorganshire valleys and the working of what was 

 practically a virgin coal-field. On June 8, 1891, in the House of Commons, Lord 

 Swansea (then Sir Hussey Vivian) asked the Vice-President of the Council whether, 

 m view of the great importance of the South Wales and Monmouthshire Coal-field 



' Memoir of Sir Andrew Cromhie Ramsay, by Sir Archibald Geikie, 1895 p 42 

 London, 8vo. 



- Revisions chiefly of the Secondary Rocks in 1864, 1871, and 1872 

 5 An article in the Times of July 24, 1862, by Dr. Percy, quoted in Ufe of Sir 

 William E. Logan, Kt., LL.D., F.E.S., F.O.S., by B. J. Harrington, 1883 n ^49 

 London, 8vo. i jjj^ p. 127^ ' ^' ^- 



