POSTGLACIAL MOVEMENTS ABOUT LAKE ONTARIO 715 



Discussion 



Prof. D. W. Johnson wished to know how far errors in determining the 

 ancient water plane at different places along the abandoned shorelines would 

 introduce errors into the determinations of presence or absence of present 

 tilting. 



Referring to a question raised by Professor Davis, Professor Johnson pointed 

 out that Goldthwait's work on the abandoned shorelines along Lake Michigan 

 seemed to show that ancient tilting did not affect the southern part of that 

 region, but increased toward the north. 



Dr. Spencek replied : In determining the deformation by triangulation of the 

 heights of the tilted beaches at various points, the measurements are very close 

 and the figures large, so that for all points west of Watertown the results 

 practically eliminate the personal equations. East of Watertown fuller meas- 

 urements may slightly modify the results, but these may be taken as approxi- 

 mately correct. 



While the location of the maximum deformation is near latitude 49° north, 

 longitude 76° west, the axis appears to follow that of the Laurentian High- 

 lands, as suggested by Dana and Goldthwait. Accordingly, the deformation in 

 the Michigan and Superior district trends to the mountain zone west of the 

 region of maximum deformation, which is the most southern lobe of the Lau- 

 rentian Highlands. The same should be true for the country to the east. 



While the rate of movement increases to the northeast or north, it decreases 

 to almost zero about the head of Lake Erie and Lake Michigan, so that the 

 deformation disappears in the interior of the continent. All of these features 

 are found in the tilted beaches of the Lake region, beyond which other data 

 must be sought to elucidate the recent earth-movements ; but some of these are 

 at hand. 



NATURE OF THE SUBSTANCE KNOWN AS MOTHER OF COAL AND ITS 

 RELATION TO THE PROCESS OF COAL FORMATION 



BY EDWARD C JEFFREY * 



(Abstract) 



In the greater number of coals there is present a substance variously known 

 as "Mother of Coal," "Fusain," "Faserkohle," etcetera. This has generally 

 been interpreted as the charred remains of wood or as the remains of woody 

 structures which have escaped the process of carbonifieation. to which the 

 woody tissues in general are subjected in coal. As the result of the investiga- 

 tion of coal by improved methods, which permit of the preparation of success- 

 ful sections, even of the most resistent coals, such as anthracites, etcetera, the 

 author has satisfied himself, by the examinations of coals of wide geological 

 and geographical range, that the so-called mother of coal is in reality the 

 charred, or partially charred, vestige of woody structures. Its presence in the 

 coal is accordingly an interesting problem. It has been made out in all the 

 cases yet examined that mother of coal is invariably accompanied by large 

 quantities of flattened spores, and the general structure of the coals in which 



1 Introduced by David White. 



