2 22 ABSTRACTS 



the Nipissing Great Lakes endured for a relatively long period of time. 

 And so long as it lasted, Niagara had only the discharge of Lake Erie. 

 A detailed account of the scoured bowlders appears in the current 

 (March) number of the American Journal of Science. 



The Grain of Rocks. By Alfred C. Lane. 



The grain of rocks is dependent on the chemical composition and 

 the causes that produce solidification, cooling, gas diffusion, etc., the 

 general law being, the more rapid the action the finer the grain. The 

 paper discusses the grain from the threefold standpoint of theory, 

 observation upon the Keweenawan rocks, and experiment. 



In regard to chemical composition, the augite of the luster-mottled 

 melaphyres shows plainly the empirical law that the less there is of it 

 the finer is its grain, other things being equal. 



The following laws of cooling are mathematically applicable to an 

 indefinite sheet : 



(/i) The case where we consider the adjacent rock symmetrically 

 heated by the sheet can be solved by aid of a solution for the case that 

 the walls are kept at a fixed temperature. For the temperature at any 

 point P of the affected zone A D (the sheet and its contact zone) is 

 the average of the temperatures that two points P^ and P^ would have 

 that were at the same distances from the walls of a hypothetical dike 

 E F, as broad as the whole zone affected (its walls being kept at a con- 

 stant temperature) as the point whose temperature is sought is from 

 the two walls of the smaller sheet ; the sum of the temperatures being 



A B P_ C D 



Pi A 



E F 



taken if said point is within the small dike, the difference if it is out- 

 side in the contact zone (time and initial conditions being the same). 



{B) Taking the case of a sheet originally of a uniform temperature 

 where the sides of the sheet are kept at a fixed temperature, we can 

 •divide the cooling into three periods : 



(i) Before the center has cooled appreciably. During this period 

 the rate of cooling is as the square of the distance of the margin, and 

 independent of the size of the sheet otherwise. 



The augite of the Keweenawan ophites follows in its grain this law, 

 the average area of cross sections being proportional to the square of 

 the distance from the margin, and independent of the size of flow. 



