REVIEWS 119 



in their papers upon the geology of the region. The effect of this 

 assumption has been far-reaching and has profoundly affected the 

 mapping during the past twenty years, so that faults have in but few 

 instances been entered upon the maps. The study by the writer in 

 the summer of 1899 of the complexly faulted basin of Newark rocks 

 lying within the Pomperaug valley in Connecticut, and the considera- 

 tion of the work of others upon the Newark areas to the east and to 

 the southwest of the New England crystalline belt, led inevitably to 

 the conclusion that a system of joints and faults produced in post- 

 Newark time must have been superimposed upon the earlier structures 

 produced by folding, and perhaps by faulting also, within the inter- 

 mediate belt of crystalline rocks. The problem was then to find 

 means of recognizing these faults within the complexly deformed 

 province. The methods which have been found available are depen- 

 dent, not so much upon the location of individual faults by the 

 ordinary means, though such methods have not been overlooked, but 

 by the reading of the fault system as a whole through the study of the 

 topography, drainage, known formation boundaries, joint system, etc. 

 Five small and widely separated areas were selected in the crystalline 

 belt within each of which a considerable number of formations were 

 found in small masses in juxtaposition. The structure of these areas, 

 while difficult to determine, was found in each case to require only 

 patience and industry, whereas the areas in which formations were 

 found in larger masses by their very simplicity of areal distribution 

 generally allowed several equally adequate explanations. 



Briefly to summarize, it may be stated that in all of the areas 

 a system of joints in correspondence with a system of faults was found 

 superimposed upon the older folded structures of the region. The 

 relative importance of deformation by folding and by faulting within 

 the region in question is somewhat difficult to estimate, but it seems 

 probable that the present attitudes of the rocks are at least as largely 

 to be accounted for by the fault structure as by the system of folds. 



O71 a Record of Post-Newark Depressio7i a?id Subsequent Elevation 



Preserved in tJie Crystalline Rocks of Neiv England. By 



William H. Hobbs. 



Along the course of the Housatonic river, between the townships 



of Sheffield, Mass., and Salisbury, Conn., is found a somewhat 



remarkable belt of largely silicified dolomite whose length is not 



