14 J. Barrell — Relations of Subjacent Igneous 



basic igneous rocks have suffered hydration and have 

 surrendered their lime to the carbonic acid which per- 

 vaded them. The degree of anamorphism appears, there- 

 fore, to be here conditioned upon depth and contiguity to 

 batholithic masses, not upon the intensity of the 

 deformation. 



The Section across Southwestern Connecticut. 



It has been shown that in passing westward from the 

 Connecticut Valley one crosses a Jurassic anticlinorium 

 leveled by later erosion. One transects also the struc- 

 tures imposed by earlier deformations, so that the actual 

 depth at which occurred the metamorphism of the rocks 

 of any given locality is difficult to state. It is clear, 

 however, that the great faults which cut diagonally across 

 the Connecticut Valley at Meriden largely die out on 

 entering the western metamorphic province. This is 

 shown by the moderate offsets of the western margin as 

 compared to the great offsets and repetitions of the 

 strata in the middle of the valley. Doubtless distributive 

 faulting in the western province occurs and some greater 

 faults may be concealed by. the complicated structures. 

 The Pomperaug Valley, holding Trias sic strata in the 

 midst of the anticlinorium, shows that it is by no means 

 a single great structural arch. Nevertheless, the regional 

 dip of the Triassic floor gives strong suggestions that 

 on passing west from New Haven to Bridgeport or Derby 

 one goes progressively into regions once deeper in the 

 crust. It is as if the railroads were inclines at slopes 

 of 5°, 10°, or 15° leading from the upper world down- 

 ward into the abyss. The exposures are best on the New 

 Haven-Derby trolley line. t\^iat, then, are the changes 

 to be observed in the nature of the rocks ? 



At the eastern contact, the least altered sheets of 

 porphyrite are found and quartz infiltrations are rare. 

 One to two miles west, the cleavage is much more pro- 

 nounced and uniform. Considerable silicification is 

 present and quartz lenses occur in discontinuous strings, 

 having deformed the chlorite schists by the power of 

 their crystal growth. One passes then into the Orange 

 phyllite, a soft black crumpled slate. Some three miles 

 farther west, the first sheets of the biotite granite 

 porphyry appear, interbedded vertically in the highly 

 foliated sediments. Within a few hundred feet of the 



