706 ABSTRACTS OF PAPERS 



PETROLEUM FIELDS OF NORTHEASTERS MEXICO BETWEEX TEE TAMES1 

 AXD TUXPAX BITERS ' 



BY I. C. WHITE 



Published as pages 253-274 of this volume. 



Discussion 



Mr. F. W. De Wolf : This is the first time I have learned of the occurrence 

 of petroleum in close relation to igneous rocks. The matter is especially inter- 

 esting to me because of the occurrence in southern Illinois of igneous dikes 

 which rise through formations which in adjourning counties yield petroleum. 



I recently learned of a coal mine in which the coal is partly coked by a dike 

 and in which there is said to be considerable gas. The gas is apparently not 

 methane, but. at least to a large extent, hydrogen sulphide, which may have 

 come from a lower oil-sand. 



INADEQUACY OF THE SAPROPELIC HYPOTHESIS OF THE ORIGIX OF COAL 

 BY EDWABD C. JEEFBEY ; 



tATjstra 



Potonie in particular has maintained that certain coals designated sapro- 

 pelic, laid down under open water, are largely composed of the structural and 

 chemical remains of Alga?. It is clear, as the result of the employment of 

 improved methods of investigation, that the structural elements in question 

 are not Algae at all. but the snores of extinct Vascular Cryptogams. It is 

 further claimed by Potonie that coals of dull and waxy appearance and con- 

 choidal fracture alone belong to the group of subaqueous coals and that coals 

 presenting alternating bands of dull and bright substance represent successive 

 epochs of terrestrial and aquatic deposition. This German authority likewise 

 maintains that coals entirely bright in appearance and of more or less pris- 

 matic fracture are of exclusively terrestrial or humic origin : or, in other 

 word*, represent the consolidated remains of former peat bogs. The purpose 

 of the present communication is to show that no adequate idea of the structure 

 and mode of formation of coals can be obtained from geological evidence alone. 

 Thin sections prepared by modifications of biological methods make it quite 

 clear that the dull or bright appearance or conchoida! or prismatic fracture 

 of coals presents no reliable index of their composition and mode of formation, 

 mpanying photomicrographic illustrations make it obvious that nearly all 

 <-oals. contrary to almost universally accepted opinion, have been formed under 

 open water and very few indeed terrestrially as peat bogs or accumulations 

 of humus. 



1 Presented at the meeting under the title "Gulf Coast petroleum fields of Mexico be- 

 tween the Tamesi and Tuxpan rivers.'' 

 * Introduced by David White. 



