Geological Society of America. 153 



augite and other constituents along the original fracture planes, which were probably, 

 in part, determined by the arrangement of the two chief constituents. 



The points of interest brought out in the study are : (i) that this peculiar dis- 

 tribution of the pyroxene is due to dynamic processes, (2) the importance to be at- 

 tached to the process of solution and recrystallization in the formation of gneisses, 

 (3) the significance of the original character of the rock with reference to the product 

 derived from it by dynamic processes, and the differences resulting from variations in 

 the extent to which it has been affected by orographic agencies, and (4) the evidence 

 showing the derivation of a gneiss out of a syenite, and establishing the term syenite- 

 gneiss as the name of a distinct rock type. 



14. 7 he Titaniferous Iron Ores of the Adirondacks. Prof. f. Kemp, New York 

 City. 



The paper opens with a brief statement of the characters of the two kinds of iron 

 ores which are afforded by the region, the merchantable magnetites and the titani- 

 ferous. The former are in gneisses ; the latter in the gabbros and anorthosites of 

 the Norian, which are believed to be intruded through the gneisses. A list of 

 localities of the titaniferous ores is given and distinction is made between the smaller 

 bodies which are, so far as can be seen, basic developments of gabbro, and the enor- 

 mous ore bodies at the old Adirondack Iron works, in the heart of the mountains. 

 These latter are in massive, anorthosite, which is almost entirely formed of large, 

 blue-black crystals of labradorite. The largest ore body, which is the one crossing 

 Lake Sandford, contains numerous included labradorite crystals, each of which is 

 surrounded by a reaction rim 5-10 mm. across. It is further shown that the wall 

 rocks show no signs of the widespread crushing that is exhibited in the general 

 "mortar-structure" of the Adirondack and Canadian anorthosites but are plutonic 

 rocks, free from evidences of dynamic metamorphism. The argument is then made 

 that the ores are segregations from an igneous magma formed during the process of 

 cooling and crystallization. 



fj. The Decomposition of Rocks in Brazil. By J. C. Branner, Stanford Uni- 

 versity, Calif. 



I 6. The Bearing of Physiography on Uniformitarianism. By Prof. W M. Davis, 

 Cambridge, Mass. 



The conditions and processes postulated in the physiographic study of land 

 forms Geomorphology of some authors are among the cardinal principles of uni- 

 formitarianism. The success in the interpretation of nature by means of this kind 

 of study confirms the correctness of its postulates, and thus brings to the support of 

 uniformitarianism a large class of facts, whose bearing on this theory was not at all 

 perceived when its early advocates announced it. 



77. Analysis of Folds. By Prof. C. P. Van Hise, Madison, Wis. 



As ordinarily treated folds are considered as simple flexures in two dimensions. 

 As they occur in nature folds are compound flexures in two dimensions. The anal- 

 ysis of simple folds given by Margerie and Heim is summarized. For the sake of 

 simplicity folds are first treated in two dimensions. A composite fold is produced 

 by the combination of various simple folds. Composite folds include both normal 

 composite folds and abnormal composite folds. The genesis of each is discussed, and 

 each is classified into upright, inclined, and overturned anticlinoria and synclinoria. 



When composite folds are cross folded, these are called complex folds. The 

 character and origin of complex folds are discussed. Rules are given for observation 

 in regions which are folded in a complex manner. The use of folds in the discovery 

 of unconformity and the secondary changes which accompany folding are summarized. 



