198 



TRANSACTIONS OF THE 



tingdon. By this arrangement a basin of red sandstone and 

 red shale is placed parallel with a part of Kishacoquillas 

 valley, on the north side of Stony mountain. 



I have accompanied this article with a variety of illus- 

 trations, because the case before us may be taken as an 

 example of similar phenomena occurring in the transition 

 ranges of this country. There is reason to believe that 

 other ancient lakes and systems of lakes have existed, and 

 have been similarly drained of their contents ; that great 

 modifications of surface have been effected among the 

 deposits of that age, even after they had acquired their 

 present position ; and that more than one of the now 

 empty basins and deep fertile valleys, enclosed between 

 some of these long parallel ridges, were at one period 

 filled with water. Penn's valley, the most elevated 

 limestone valley in Pennsylvania, and considerably the 

 largest in this part of the state, shows indications of having 

 been formerly filled with water to a great height, such 

 waters having subsequently effected their escape by two 

 strongly defined outlets. We shall probably have occa- 

 sion to return to this subject hereafter. 



The illustrations prepared for this article are — 

 1st. A map of Kishacoquillas valley and its vicinity. 

 PI. 9, fig. 1. 



2d. A transverse geological section across its centre. 

 PI. 9, fig. 2. 



3d. PI. 8, fig. 3. A view from the small central 

 limestone eminence looking east, showing the eastern ter- 

 mination of the ancient lake, at the point B, shown also 

 in the map pi. 9, where the interior ridges unite with 

 Jack's mountain, on whose side is traced the shelf formed 

 by the ancient beach. It also illustrates a very character- 

 istic feature in this country, showing the conical hills, 

 called gables, being the truncated or transverse sections 

 of some of those numerous parallel ridges which range 

 through central Pennsylvania. 



