The Legacy of Charles Lyell: Advances in Our Knowledge of Coal and Coal-Bearing Strata

Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 The legacy of Charles Lyell: advances in our knowledge of coal and coal-bearing strata ANDREW C. SCOTT Geology Department, Royal Holloway University of London, Egham, Surrey TW20 OEX, UK Abstract: On his travels in both Britain and North America Sir Charles Lyell paid particular attention to coalfields and their fossils. Understanding the formation of coal and associated rocks was the subject of several publications. In this contribution three aspects of this work are highlighted, all of which are the subject of ongoing modern research. Lyell was interested in modern analogues for the Carboniferous coal swamps and was amongst the first to suggest analogies with the mires of the eastern United States, such as the Dismal Swamps. A brief review of recent research on new modern analogues from Southeast Asia is presented. Lyell observed 'mineral charcoal' in some of the coals and noted its anatomical structure. Considerable advances in our understanding of the role of fires in terrestrial ecosystems and their potential as an agent of fossil preservation are addressed. One of Lyell's most important palaeontological finds was of remains of the earliest reptiles (these proved to be amphibians but Sir William Dawson found reptiles subsequently) preserved in the Upper Carboniferous tree trunks at Joggins, Nova Scotia, Canada. Whilst this occurrence of reptiles is no longer the oldest, the reasons for the remarkable tetrapod occurrences in upright sandstone-filled lycophyte trees at Joggins are currently being investigated and recent progress is presented. Throughout his life, Sir Charles Lyell was fascin- of the fossils he found were undertaken by the ated by the study of coal and coal-bearing strata. leading palaeontologists of his day. The study of coals and coal fields was not only the subject of numerous papers but also became a major feature of his travels in North America. Historical background Indeed, coal was a strategic material at the time and was the subject of several lectures that Lyell made The nature and origin of coal has remained a field during his visits to North America. Some of his of study for over 200 years and even today many researches, such as the discovery with Sir William fundamental questions concerning coal have yet to Dawson of tetrapods within upright lycophyte be satisfactorily resolved. Although this is indeed a trunks at Joggins, Nova Scotia (Lyell 1853a; Lyell very complex problem, geologists at the end of the & Dawson 1853), remain as important now as then eighteenth and beginning of the nineteenth century (Carroll 1994). Many of the problems which Lyell considered the possibility of simple solutions. One attempted to address are still the subject of ongoing can consider the origin of coal as comprising three research. While some of the problems addressed by basic problems. First, there is its composition- Lyell, such as the age and structure of various whether in fact coal is formed from vegetable or coalfields, have largely been solved, others are still mineral material. Second, if its origin is vegetable the subject of intense research and debate. is coal formed from in situ or drifted plant remains? In this contribution three major research topics Third, there is the question of coal's diagenesis - are highlighted: the origin of coal together with the processes that affect the material during burial evidence of the fauna and flora of coal measures; (the coalification process - the conversion of peat the occurrence and significance of charcoal in coal into coal by heat and pressure). The solution to each seams; and modern analogues for ancient coals. In problem requires information from both laboratory each of these three topics it is important to recog- and field observations. In the latter half of the nize that background data were limited. It is eighteenth century many authors lacked basic interesting to note, however, that Lyell understood experience of field work. the limits of his expertise and called upon the By 1780 a number of authors, particularly on the services of other researchers so that the descriptions continent (De Buffon and De Luc in France and ScoTt, A. C. 1998. The legacy of Charles Lyell: advances in our knowledge of coal and coal-bearing strata. 243 In: BLUNDELL,D. J. & ScoTr, A. C. (eds) Lyell: the Past is the Key to the Present. Geological Society, London, Special Publications, 143, 243-260. Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 244 A.c. scoyr Baron van Beroldingen in Germany) had recog- Brown in Haliburtons 'Nova Scotia' (Lyell 1843). nized the vegetable origin of coal (Stevenson 1911; The work of Brown and Logan contributed to Bennett 1963). This idea of a vegetable origin was establishing that Carboniferous coals were formed first accepted in Britain by Hutton (1795). Hutton by vegetation living in situ (see for example Binney considered that coal was formed by the deposition 1846; Brown 1846, 1848; Logan 1841; Lyell 1841). of vegetable material in the sea and that it was Lyell became interested in all aspects of the subsequently heated to form coal. Opposed to this Carboniferous coal measures in particular, from the view, however, was the Irish chemist Richard plants and animals preserved associated with the Kirwan (1799) (championing the mineral origin of coals, trace fossils, sediments, to the structure of the coal) who was in turn vehemently attacked by coal basins (Lyell 1846a, b, c, d). A key to the James Parkinson (1804). By the time of the development of his thoughts on the origin of coal- publication of the first edition of Lyell's Principles bearing sequences was the visits Lyell made to the of Geology (1830-1833) the vegetable origin of coalfields of North America and to Nova Scotia in coal was firmly established. In Volume 1 of the particular. Principles Lyell made only four references to coal Lyell first visited the superb exposures of Upper strata, in Volume 2 (1832) he made only one Carboniferous Coal Measures along the Bay of reference to coal formation and in Volume 3 (1833) Fundy in Nova Scotia in the summer of 1842. He only one reference to coal alteration. writes (1845, vol. 2, p. 63), At the time of the publication of Volume 2 of the Just returned from an expedition of 3 days to the (1832) there was considerable support Principles strait which divides Nova Scotia from New for the drift origin of coal, which would have given Brunswick, whether I went to see a forest of support to the diluvialsts. Lyell (p. 242) writes, fossil coal - trees - the most wonderful pheno- Notwithstanding the vast forests intercepted by menon perhaps that I have seen, so upright do the the lakes, a still greater mass of drift-wood is trees stand, or so perpendicular to the strata, in found where the Mackenzie reaches the sea, in a the ever-wasting cliffs, every year a new crop latitude where no wood grows at present except being brought into view, as the violent tides of a few stunted willows. At the mouths of the river the Bay of Fundy, and the intense frost of the the alluvial matter has formed a barrier of islands winters here, combine to destroy, undermine, and and shoals where we may expect a great sweep away the old one - trees twenty-five feet formation of coal at some distant period. high and some have been seen of forty feet, piercing the beds of sandstone and terminating The drift versus in situ hypothesis of the origin of downwards in the same beds, usually coal. This coal was of considerable interest to Lyell. His field subterranean forest exceeds in extent and quality observations on coal and coalfields played an of timber all that has been discovered in Europe important role in developing his ideas which were put together. more prominently discussed with each edition of his Principles and later his Elements and Manuals. Lyell provides a detailed account of his visit to Following his visits to North America to study the section at Joggins (Lyell 1843). He not only coalfields, and especially with his experiences at notes the occurrence of several levels of trees but Joggins, Nova Scotia, Lyell expands his entries on also some of the fauna and flora associated with the coal to nine by the ninth edition (1853b) and the coals. Lyell (1843, p. 178) draws several con- fifth edition of his Manual of Elementary Geology clusions from his observations of the Joggins (1855b) contains 18 entries on coal and coalfields sequence: which includes detailed descriptions of in situ trees, 1. That the erect position of the trees, and their the use of modern analogues and also a discussion perpendicularly to the planes of stratification, of fire. imply that a thickness of several thousand feet of coal strata, now uniformly inclined at an angle of 24 ~ were deposited originally in a horizontal position [see Fig. 1]. The origin of coal and the associated fauna 2. There must have been repeated sinkings of and flora the dry land to allow of the growth of more than By the time of the studies of Lyell, although the ten forests of fossil trees one above the other, an botanical origin of coal had been firmly inference which is borne out by the independent established, the nature of the accumulation of the evidence afforded by the Stigmaria, found in the plants was widely debated. Lyell noted (1843) underclays beneath coal-seams in Nova Scotia, mention of upright fossil trees in the coal measures as first noticed in South Wales by Mr. Logan [see of Joggins in a paper published in 1829 by Richard Fig.

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