JEFFREY. — NATURE OF SOME SUPPOSED ALGAL COALS. 277 



line. Figure 2, Plate 1, shows the same coal in section parallel to the 

 planes of layering under the same microscopic enlargement. The 

 spores appear in this plane in rounded outline and are much fewer in 

 number. The explanation of the circular outline and the smaller 

 number of apparent spores is afforded by the vertical section. In 

 many cases it is possible in sections parallel to the layering of cannel 

 to make out the presence of spores still in tetrads or in the case of 

 isolated spores to distinguish triradiate ridges resembling those which 

 mark contact surface of the reproductive bodies in many living vascu- 

 lar cryptogams. Some instances of these appearances are illustrated in 

 the subsequent parts of this article, and need not be discussed here. 

 The cannel just described is from Kentucky and is quite tj^ical of the 

 coals of this nature derived from this and other States. European 

 cannels have also been studied but in general they show structure less 

 clearly than the American cannels which have been examined. This 

 is perhaps one of the causes of the apparent misinterpretations of some 

 of the European writers on the microscopic structure of coal. 



The Structure of Kentucky Boghead. 



In most of the samples of cannel coal from Kentucky which have 

 come under my observation, there occur, to a greater or less extent, 

 bodies generally pale yellow in color but sometimes brown. These 

 viewed in certain planes of section have the alveolar appearance, which 

 is characteristic of the supposed Algae of Betrand, Renault, and Po- 

 tonie. Those coals in which the imagined Algae become most abun- 

 dant are known as bogheads, in accordance with the terminology of 

 Renault. 



It has been considered desirable in this connection to illustrate a 

 boghead of unquestionable authenticity. I am indebted to Dr. David 

 White of the United States' Geological Survey for some excellent ma- 

 terial of Kentucky boghead of Pottsville age, which has been utilized 

 in making the figures which are described in the paragraphs imme- 

 diately following. A comparison with the figures and descriptions of 

 Renault's monumental work show clearly that it is his Pila ken- 

 tucki/ana or a very closely allied species. 



Figure 3, Plate l, shows a number of the supposed Algae, denomi- 

 nated under the generic appellation Pila, somewhat highly magnified. 

 They are variously grouped and scattered throughout the figure, a 

 particularly striking clump appearing on the upper left hand of the 

 figure. Most of the individuals show a mottled appearance, the dark 

 spots corresponding in position to the supposed agal individuals con- 



