12 J. Barrell — Relations of Subjacent Igneous 



this axis in western Connecticut is unknown. Neverthe- 

 less, the breadth and dip of the crust blocks show that the 

 elevation was great, notwithstanding that peneplanation 

 had ensued by the beginning of the Comanchean. 



The Connecticut Valley is the foot of the eastern slope 

 of this Jurassic anticlinorium. As a result of later 

 base -levelling across this, on going west from the edge 

 of the valley one passes progressively into rocks origi- 

 nally deeper and exposed by successive cycles of post- 

 Newark erosion. On the edge of the Connecticut Valley, 

 as Davis was first to note, is exposed the old Triassic 

 floor upon which the basal Newark sediments were laid 

 down. Here there has been no erosion since the mid- 

 Triassic beginning of the Newark sedimentation. It is 

 physiographically the nearest to the surface of the earth 

 in the Appalachian revolution of any part of western 

 Connecticut. Wliat, then, is its character? In the 

 northern half, two granite bosses outcrop, each about 

 four miles in diameter. The northern especially is asso- 

 ciated with more or less fine-grained intrusive amphibo- 

 lite. The country rock is a lustrous sericite schist, be- 

 coming coarse-grained where penetrated by pegmatite 

 dikes and dikelets. In the southern part of this border 

 zone, the Prospect gneiss is intersected. This is a belt 

 exposed for more than thirty miles, with an average 

 width of two miles, and striking slightly diagonal to the 

 contact. It consists of sheets of slightly gneissoid coarse 

 biotite granite porphyry. The texture is highly variable, 

 and it seems to have been intruded in successive sheets. 

 It does not widen in passing away from the Triassic floor 

 into what was presumably greater original depth. It 

 appears, then, to have been a great dike intrusion, rather 

 than a batholith. South of this occurs a dark slate, the 

 Orange phyllite, containing quartzitic and calcareous 

 beds. This is the least metamorphosed sedimentary 

 formation in western Connecticut. South of this is found 

 the Milford chlorite schist, extending to Long Island 

 Sound. This is a hydrothermally altered series of basic 

 sheets, strongly resembling the Keewatin chlorite schists, 

 though of Paleozoic and probably of late Paleozoic age. 



The topography of this area is in detail rugged, sheets 

 of feldspar porphyrite (now slightly altered) having 

 been injected into a previously mashed series of much 

 the same composition. The older and thoroughly chlori- 

 tized portions are probably only slightly older, as shown 



