194 
Leaving the little GbSErVatOry, the path follows along the brink 
ort ama 
gorge, looking northeast. The accompanying illustration gives 
idea of this, but only a visit to the spot will make one re- 
alize its beauties. On either side are perpendicular walls of rock, 
beautifully variegated by alternating strata of shale and sand- 
stone, rising to a height of three hundred and fifty feet, twenty 
feet higher than the palisades opposite New York City, crowned 
on the left bank with a mass of vegetation to an additional 
height of one hundred and fifty feet, making the total on that 
side nearly five hundred feet. 
This gorge of the Genesee is often known as the Portage 
gorge, and these rocks, laid down nearly fifty million years ago, 
belong to the Portage epoch of the upper Devonian age. Most 
of what is now New York state then lay under a vast sea. The 
rivers of what land there was at that time washed their sediment 
down into this apparently shallow sea where it settled and formed 
not only the Portage rocks but also others of central and western 
New York. As time passed on, other and more modern strata 
were laid down on this Portage formation, burying it out of 
sight. Ages passed, and finally came a great upheaval of the 
continent, when the bottom of this sea was raised up and dry 
land was formed. As the center of this upheaval was to the 
north, the strata, which were formerly horizontal, assumed a 
gentle dip to the south. Then the elements attacked the land; 
eroded, until finally in millions of years the Portage rocks were 
again brought to view 
About the time of the glacial age a great depression occurred 
in the north, reversing the inclination of the land, making the 
rivers which formerly flowed to the south now take a northerly 
direction. But the glaciers, stopping up the valleys with their 
debris, formed large lakes, and one of these was located in the 
large basin-like area, a part of the old Genesee valley, to the 
south of the present Portage gorge. As the depression con- 
tinued in the north, this lake began to overflow, naturally at the 
