336 E. B. MATHEWS- 



-SUBMERGED ''dEEPS" IN SUSQTtEHANNA RIVER 



above the water. Under ordinary conditions the bed of the river is cov- 

 ered with less than 15 feet of water, and in dry season may be largely 



exposed as a rock floor from one- 

 half to one and one-half miles in 

 breadth. Within this flat bottom 

 of the broad gorge the survey dis- 

 covered (figure 1) six long spoon- 

 shaped depressions, some of them 

 over 100 feet deep, with their 

 deepest portions extending below 

 ; tide level. To record the position 

 ' and character of these "deeps,'' 

 ' and to show that the usual ex- 

 l planations for similar phenomena 

 \ do not apply, is the purpose of 

 ^ this paper. 

























// 





/ ' 





; / 





if 

 ,' j 





I it 





^^7- 





- ^^ 





- -it 





X-l\ 





t^l- 





- fn 





- t-il- 





- tj^ 









111 





i |^_^ 





/ 'l^ — ^ 









^i~t''^'^ 





•i^^^y- 



fc 



P^si- 



1 



Ia 





1 \ 





^ ^ 





i^ 



1 



Y 



1 





I 



t 



/ 



K 





"T 



;• ' 



I 



ii{ 





Ji 





ii 



, 



i 



1 1 s J ? 



ni 



Geology of the Eegion" 



The geology of the region on 

 either side of the Susquehanna 

 gorge from Columbia, Pennsyl- 

 vania, to Havre de Grace, Mary- 

 land, may be briefly summarized 

 as an overthrust block or series of 

 blocks of Precambrian schists and 

 gneisses resting on less metamor- 

 phosed limestones and shales of 

 Cambrian and post-Cambrian age. 

 The forward end of this thrust 

 forms an irregular line, crossing 

 the Susquehanna River at Turkey 

 Hill, below Columbia, and con- 

 tinuing thence eastward in a sinu- 

 ous line to Quarryville and the 

 Chester Valley. 



This block consists of several 

 fragments, separated by faults, 

 and near its northwestern edge are 

 several "fensters," through which 

 appear portions of the underlying 



