310 



Report of the State Geologist. 



and Ellicott creek take their rise and flow northward across the lower plain to 

 Tonawanda creek. The other streams which traverse the middle plain are 

 Cayuga creek and its branches, Buffalo creek, Cazenovia creek and Smoke 

 creek, the last three of which have their sources in the hill region to the south. 



The Hill Region. The elevated region comprising the remainder of the 

 county consists essentially of a high plateau gashed by streams which have 

 eroded much of the original surface and left it a succession of valleys and 

 ridges. 



In the vicinity of Chaffee. East Concord and westward, this tableland has 

 attained the height of nearly 1,500 feet A. T. From this there is an abrupt 

 slope into the valley of the Cattaraugus creek, with a more gradual descent 

 toward the north and west. From the Buffalo and Southwestern railway 

 toward the lake, the descent is very gradual and the surface smooth or gently 

 undulating, terminating at the lake shore in abrupt bluffs. Along the southern 

 crest of the plateau and extending into the Cattaraugus valley are immense 

 piles of glacial debris, giving rise to a peculiarly knolly topography. The 

 principal streams flowing westward from this region are the Big Sisters creek 

 and the two branches of Eighteen-Mile creek. In their upper courses these 

 have steep-sided valleys, and in the lower courses deep gorges with precipitous 

 Avails of rock. The ridges between the streams have smooth tops on approxi- 

 mately the same leve.L 



Stratigraphy. 



The rocks exposed in Erie county range from near the bottom of the 

 Salina shales to near the top of the Portage group. The members in their 

 order are shown in the following table : 



( Upper. 



Portage group \ T 



{ Lower. 



r Genesee slates. 



Hamilton group - Hamilton shales. 



' Mareellus shales. 



f Corniferous limestone. 

 Upper Helderberg group ... \ n 

 iA I Onondaga limestone. 



Water-lime group. 



Salina group. 



The thickness of the above rocks as ascertained by deep borings a nd 

 measurements will be given at the close of the chapter on natural gas. 



