148 PROCEEDINGS OF THE AMHERST MEETING 



evidence) to have been formed chiefly on the flanks of faulted and collapsed 

 anticlinal arches and domes resulting from the synclinal folding. The fine, 

 or lamellar, banding occasionally noted in jasperiod is explained as the result 

 of differential replacement of laminated limestone by quartz. The replacement 

 of limestone by dolomite instead of jasperiod, which is found in parts of the 

 district, is accounted for by selective metasomatism, due chiefly to slight 

 differences in the character of the deformation of the limestone prior to re- 

 placement. 



From a consideration of the chemical aspects of the problem of limestone 

 replacement and ore deposition (with special attention to the underground 

 waters of the region) the deduction is drawn that the replacement by 

 jasperoid involved dilute solutions of silica and carbon dioxide, the latter 

 having resulted largely from reaction between sulphate in solution and 

 hydrocarbons contained in the limestone, and from the reduction and precipi- 

 tation of the metals as sulphides. The bitumen of the ore deposits is con- 

 sidered a residual from rhese reactions. 



The chemical conditions favorable to the metasomatism of the limestone 

 and to ore deposition being evidently widespread, while the only structural 

 feature which api>ears to be common to all the ore deposits is the deformation 

 of the limestone, it is concluded that this deformation has been the controlling 

 factor in the replacement of limestone by both jasperoid and dolomite, as well 

 as in the deposition of the sulphides of the metals. 



Since the term jasperoid is not entirely satisfactory for such rocks as are 

 here described, and since replacements of limestone or dolomite by silica form 

 a well defined type, of relatively common occurrence, the name silekite 

 (sil'-e-kite) is proposed for such replacements, whether crystalline or chalce- 

 donic. 



Presented by title in the absence of the author. 



TRANSITIONAL COALS AND THEIR BEARING ON HYPOTHESES OF THE 



ORIGIN OF COALS 



BY EDWARD C. JEFFREY 



(Abstract) 



By improvements in methods the author has been successful in making 

 sections showing the transition from one type of coal to another. It is well 

 known to those who have given any attention to the study of coals that not 

 infrequently bituminous coal of black and shiny aspects passes abruptly into 

 dull lustered cannel. Similarly, bituminous coal passes into oil rock. (Notably 

 is this the case in certain Australian coals.) It is generally assumed that 

 most coals with a glistening or predominantly glistening aspect are formed 

 in -situ and on a more or less solid substratum. Such coals are commonly 

 designated humic coals at the present time. In contrast to these are the oil 

 shales and cannels, characterized by a dull luster. These are universally 

 admitted to have been laid down by sedimentation in open water. They are 

 currently known as sapropelic, or aquatic, coals. The study of the transition 

 from one type to the other clearly shows that the so-called humic, or terres- 

 trial, coals are practically identical in organization to the so-called sapropelic, 



