I9I3.] STEVENSON— FORMATION OF COAL BEDS. 45 



into white marl, consisting of pulverized coral. In most places, 

 where the horizon is exposed, a coal bed is seen overlying this reef 

 and often in direct contact with the limestone. Great branching 

 Stigtiiariae grew upon the rock, following all irregularities of the 

 surface as they pushed their way through the marl. Limestone 

 under brown coal is reported from the Tertiary-* as well as from the 

 Quaternary and it occurs frequently under peat deposits of the 

 Recent period. Evidently, Stigniaria cared less for the soil than for 

 other conditions, just as do many plants of this day. The relations 

 of coal to the seat are very like those observed in peat deposits, 

 where the accumulation may begin on clay, sandstone, limestone or 

 even on bare consolidated rock, if only the essential condition of 

 moisture be present. Temperature is not all-important, for peat 

 accumulates as well in the tropics as in the temperates, wherever 

 peat-making conditions exist. It fails in the tropics precisely as it 

 does in the temperates, when the peat-making conditions are absent. 

 The relations were the same in earlier periods, for Wall and 

 Sawkins^^ report their discovery of 37 coal beds in the Miocene of 

 Trinidad, of which 5 are workable, with a thickness of 19 feet; 

 and this coal-bearing formation was followed by them on the main- 

 land in an area of 36,000 square miles. And the condition still 

 exists on that mainland. Harrison-*' says that tropical peat, known 

 as '' pegass," occurs behind the fringes of courida and mangrove in 

 many parts of the low-lying coast lands of British Guiana and that 

 it is from i to 10 feet thick, though usually 2 to 4 feet. He pointed 

 out that, on the pegass land, the alternation of wet and dry seasons 

 allowed both marsh and ordinary plants to grow and that consider- 

 able areas were covered with forest of the Acta palm. 



Stigmaria is present in a great proportion of the underclays. 

 The manner of its occurrence has been described on earlier pages 

 and only passing reference is needed here. Sorby, Piatt and Daw- 



^* C. V. Giimbel, " Beitrage," etc., pp. 149-151; O. Heer, cited in "Forma- 

 tion of Coal Beds," these Proceedings, Vol. L., p. 623. 



-' G. P. Wall and J. G. Sawkins, " Report on Geology of Trinidad," Lon- 

 don, i860, pp. 112, 197. 



^'J. B. Harrison, "Pegass of British Guiana," Quart. Joiirn. Geol. Soc, 

 Vol. LXIIL, p. 292. 



