ABSTA'ACTS 223 



Consolidation in this period may a priori ht expected to be especially 

 characteristic of effusive and porphyritic rocks. 



(2) While the center is cooling down one-fourth of original dif- 

 Jference in temperature between sheet and margin. This period is 

 about four times as long as the first. 



(3) Thereafter the rate of cooling when given temperature is 

 reached will be independent of the position of a point. Hence the 

 grain will be uniform and the same for all parts of the sheet that con- 

 solidate in this period. The solidification will tend to fall into this 

 period for high initial temperatures of the magma and hot walls, com- 

 pared with the temperature of solidification and broad contact zones. 

 Hence solidification in this period may be taken as typical for abyssal 

 rocks. 



Dikes of the Keweenawan in the Huronian show a marginal zone 

 where the grain appears to have been formed in the first period of 

 solidification, and a central belt where the solidification appears to 

 have been in the third period. 



Similar phenomena may be reproduced in melted sulphur, and in 

 sugar and water. In the latter case we have phenomena of aqueo- 

 igneous fusion, and the temperature of solidification being compara- 

 tively low, there is a strong tendency toward the appearance of the 

 central zone of uniform grain. The tendency to solidify as glass is 

 dependent upon the escape of the water. 



If the sides are not kept at a fixed temperature, the sides will cool 

 more slowly than the center, for temperatures half way between the 

 initial temperatures, — a possible explanation lies here for a certain 

 kind of porphyritic facies of granites. 



A Study of the Nature, Structure, a>id Pliylogcny of Dcemonelix. By 

 E. H. Barbour. 



Additional expeditions to the Utemonelix region have added new 

 data showing the apparent steps in the phylogeny of this anomalous 

 group. 



The simplest expression of Dcemonelix seems to be a fiber found 

 in the sand rock, which shows unmistakable plant structure, and is, 

 in every respect, like the fiber found in all the Daemonelix series. The 

 author's present belief is that the various forms of the Daemonelix 

 group result from the aggregation of these simple fibrous, fresh-water 

 seaweeds into variously shaped bunches, clusters, and spirals. 



