96 THE JOURNAL OF GEOLOGY. 



"3. Eskers and sand plateaus are genetically connected ; the term, feed- 

 ing -esker, is fully warranted by the relation of the two in position, structure, 

 and composition. 



"4. The sand plateaus were made rapidly ; this is proved by the absence 

 of disordered beds at their heads, where space would have been opened by the 

 backward melting of the ice had the forward growth of the plateau been slow. 

 The eskers were also made rapidly, as is shown by their 'open -work gravels.' 



" 5 . The diversion of the feeding streams to other outlets left the plateaus and 

 the eskers without further energetic action as the ice melted away from them. 



"6. The present form and structure of the eskers are more accordant 

 with the supposition of a subglacial origin than of a superglacial origin ; but 

 it is not intended to imply that other eskers of more irregular form and dif- 

 ferent structure could not have been deposited in superglacial channels." 



H. B. K. 



Studies in Structural Geology. By Bailey Willis, U. S. Geol. Surv. 

 (Transactions of the American Institute of Mining Engineers, 

 June, 1892). 



The paper aims " to present some of the results of observation of the 

 geologists of the Appalachian division during the past three years on the 

 subject of structural geology in the Appalachian province." The structural 

 features are all of one type but of different phases, comprised in four great 

 districts, i) the district of close folding, 2) a district whose chief structural 

 characteristic is cleavage, 3) a district of open folding, 4) a district of fault- 

 ing and folding. The answer to the questions. Why did the strata bend in 

 the district of open folding, and why did they break in the district of fault- 

 ing, is that the thrust affected them according to their rigidity under their 

 respective conditions of superincumbent load. " We know that load up to 

 a certain point restrains fracture in material under thrust." In the district 

 of open folding the Devonian limestone is the most rigid of the strata and 

 " the one which would most effectively transmit the compressing thrust and 

 would control the resulting structure." Tn the district of open folding this 

 limestone was prevented from breaking and faulting by a load of superin- 

 cumbent strata exerting a pressure of 10,000 to 23,000 pounds per square 

 inch, while in the faulted district a load of 5,000 to 10,000 pounds per square 

 inch permitted the strata to break and fault. 



The answer to the question, Why did the compression affect this zone, is 

 given. " It becomes apparent on study of sections that where compression 

 raised a great arch there previously existed a bend from a nearly horizontal 

 to a descending position in the principal stratum transmitting the thrust. 

 Greater anticlines and synclines originated in upward and downward con- 

 vexity of initial dips, due to unequal deposits of sediments which depress 



