42 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



forced out of its graded bed onto rock at a higher level. Prob- 

 ably both causes have operated, but the latter has produced more 

 marked effects. 



Umpog Creek has its source in a small forked stream which 

 rises in the granite hills east of the south end of Umpog Swamp. 

 After passing westward through a flat swampy area, where it is 

 joined by the waters from Todd Pond, the stream turns north 

 and follows a shallow rock gorge until Umpog Swamp is reached. 

 The divide which separates the present headwaters of the Umpog 

 from those of the Saugatuck is a till-covered swampy flat about 

 one-quarter mile east of Todd Pond. This arrangement of trib- 

 utary streams is correctly shown in fig. 7 and differs essentially 

 from that shown on the Danbury atlas sheet. This divide owes 

 its position to the effects of glaciation. Deposits of till and the 

 scouring of the bed rock so modified the preglacial surface that 

 the upper part of the Saugatuck was cut off and made tributary 

 to the Umpog. 



THE PREGLACIAL DIVIDE 



In order to determine whether Still River flowed southward 

 through the Saugatuck Valley just before the advent of the ice 

 sheet, the borders of Umpog Swamp and the region to the south 

 and east were examined. It was found that Umpog Swamp is 

 walled in on the south by ledges of firm crystalline limestone 

 and that the rock-floored ravine leading southward from the 

 swamp, and occupied by the railroad, lies at too high an elevation 

 to have been the channel of a through-flowing stream. A south- 

 flowing Still River, and much less an ancient Housatonic, could 

 not have had its course through this ravine just previous to 

 glaciation. A course for these rivers through the short valley 

 which extends southeastward from Umpog Swamp is also ruled 

 out, because the bedrock floor of this hypothetical passageway is 

 20 feet higher than the floor of the ravine through which the 

 railroad passes. 



The eastern border of Umpog Swamp is determined by a 

 ridge of limestone which separates the swamp from lowlying 

 land beyond. This ridge is continuous, except for the postglacial 

 gorge cut by the tributary entering from the east, and must have 

 been in existence in preglacial times. The entire lowland east 



