during the melting of the Glacier. 421 
lies Birmingham, with Shelton opposite on the west (or south- 
west) bank of the Housatonic, and the village of Derby on the 
east bank of the Naugatuck. The streams rise in the high re- 
gions of Western Massachusetts and Connecticut, in part over 
1000 feet above the sea, and flow in rapids through much of 
their course down to their confluence, where they reach tide- 
level, ten miles from the Sound. 
As Birmingham is but nine miles to the westward of New 
Haven, it is improbable that the amount of elevation which the 
two places have undergone since the Champlain or Fluvial pe- 
riod should differ much; and hence there must be a special 
cause for the great height of the Housatonic terrace. For this 
cause we have only to look to the topographical conditions of 
the region. 
Besides the fact of (1) the junction there of two rapid 
streams, whose united drainage area is about 1800 square miles, 
there are the following additional facts bearing on the subject : 
(2) Both streams at that place have narrow terrace regions, the 
valleys between the hills having little width—(3) On the east 
side of the Naugatuck the high bordering hills leave almost no 
1 iy at their foot for the one-street village of Derby, so that 
e flooded waters cannot spread in that direction, and are nat- 
urally forced over against Birmingham and Shelton.—(4) The 
hills that lie back of Shelton, embaying its terrace region, reach 
to the river just below the village, and so do those on the 
Derby side, making thus, below Derby, a comparatively con- 
fined verny for the united waters, which has long been called 
the * erby Narrows.”—(5) The river channel below Derby, 
through its ten miles to the Sound is very shallow, being navi- 
gable for vessels drawing four feet of water only at high tide ; 
‘nder such circumstances it is natural that the waters of the 
Glacial flood plunging down the two valleys should have en- 
tered the region of Birmingham and Shelton faster than they 
could have escaped. The fact that a cataract of great volume 
, the region of Birmingham and dashed violently against 
the Shelton shore is abundantly manifested by the multitudes 
of large water-worn rocks and thick coarse cobble-stone de- 
Posits in the upper portion of the lower as well as high upper . 
ot and in the imperfect stratification of portions of the 
ven modern floods in the region bring down waters faster 
than ee are discharged Rin the Derby Narrows and the 
channel eyond. The Housatonic river below the confluence 
