Southwestern New England Region. 441 



them, and are, moreover, by reason of the most cordial personal 

 relations desirous of securing perfect harmony of view. From 

 examination of himself, no less than of others, the Writer is 

 inclined to believe that confidence in any structure worked out 

 in the region upon a doctrine of deformation by folding alone 

 is more largely based upon psychological than upon geological 

 conditions ; and this for the reason that a feeling of confidence 

 inspired by observation at one locality has too often been 

 quickly and most effectually dispelled by the next succeeding 

 observation at an adjacent exposure. In the study of the 

 structure within the gneiss belts there are two main tendencies 

 which in varying proportions will be found to characterize the 

 work of different geologists. One tendency is to group 

 together within a single formation a considerable number of 

 variant types of gneiss because no apparently satisfactory basis 

 for their separation is at hand ; and as the work progresses it 

 is found that all the types of one formation can be duplicated 

 in the others. The other tendency is to make an elaborate 

 differentiation of units on a petrographical basis, with the 

 result that extreme difficulty is met with in accounting for the 

 present attitudes of the rocks, and large drafts must be made 

 upon the imagination. At different points between the two 

 horns of the dilemma different workers will very naturally be 

 ranged. 



The Newark Areas in their Relation to the Crystalline Belts. 



In the summer of 1899 the writer, in surveying for folio 

 publication the areas for 3.0" quadrangles, mapped with much 

 detail the circumscribed area of Newark rocks lying within 

 the basin of the Pomperaug River in Connecticut. These for- 

 mations of the Newark system present markedly contrasted 

 petrographical types, are practically unaffected by flexuring 

 or metamorphism, but exhibit in the most beautiful manner 

 the results of a deformation by jointing and normal faulting. 

 After long attempts to decipher the obscure and illegible 

 characters in the structure of the surrounding gneiss belt, the 

 transition to the clearness and simplicity of the record pre- 

 served within the Newark basin was like the passage from 

 darkness to light. The study of the Newark area showed that 

 it was deformed by a complex system of parallel and intersect- 

 ing faults all near the vertical, and that the system of joints 

 which preceded and conditioned the system of faults was with 

 little doubt the result of compressive stresses which affected 

 the southwestern New England province as a whole. The 

 principles underlying such a deformation by fracture as a result 

 of compressive stress have been given a somewhat full exposi- 



