THE RIVER SYSTEM OF CONNECTICUT 4/1 



The detailed study of the Pomperaug Valley area has devel- 

 oped the fact that a complex system made up of intersecting series 

 of parallel nearly vertical joints and faults there divides the crust 

 into a large number of orographic blocks, the smaller of which 

 have dimensions of less than one hundred paces. The different 

 throws along the numerous faults bounding these blocks have 

 brought about a structure not unlike that of a mosaic from 

 which the supporting base has been lowered and the individual 

 stones been displaced by different amounts due to the inequali- 

 ties of their lateral support. For the area as a whole, the joints 

 and corresponding faults are embraced mainly in four series, the 

 individual members in which trend N. ± 34° W., N. ±55° E., N. 

 zt 5° W., and N. ±: 15 E. Series of faults less common for the 

 area as a whole, but several of them numerous enough in its 

 southern portions, have directions N, ±: 33° E., N. dz 44° W., N. 

 ± 61° W., N. ± 90° E. W., N. ± 20° E., and N. ±; 25° W., the 

 order being approximately that of frequency of occurrence. Of 

 the more common series, those trending N. ± 55° E. and N. ± 

 34" W. are nearly normal to one another, as would be true of a 

 pair of joint planes, but the larger throws within the region seem 

 generally to have taken place along one of these planes (N. rt 

 55° E.) and one of the other prevailing directions (N. rt 5° W.) . 

 Aside from the regularity in direction observed to characterize 

 the numerous faults and bring them into a number of parallel 

 series, those faults of the same order of displacement are 

 observed to be spaced also with noteworthy regularity. The 

 smallest of the orographic blocks which could be measured, for 

 convenience called the " unit " blocks, were found to be quite gen- 

 erally about 50 paces (150 feet) along the direction N. ± 55°E., 

 and 100 paces (300 feet) along the direction N. ± 5° W. — the 

 equivalent of two rhombic prisms in contact along one side. 

 The larger, or "composite" blocks, which are of various orders 

 of magnitude, are made up of the "unit" blocks and bordered 

 by displacements of a higher order — greater throw. The fault 

 intervals in the several series, and hence the shapes of the oro- 

 graphic blocks, are found to be closely related to the directions 



