8 THE AMERICAN MUSEUM JOURNAL 



which has been placed beside the local rock collection in the 

 Hall of Geology. The collection has been arranged in two cases. 

 One of these shows the kinds of rocks encountered when crossing 

 the island from east to west at several points, while the other 

 shows nearly all the varieties of rock which have been found in 

 ledges on Manhattan Island. Three sections of borings, further- 



QUARTZOSE VEIN IN MICACEOUS GNEISS 



West End Avenvie near Sixty-third Street. Specimen is 5i inches across. 



more, show the rock found at considerable depths at widely 

 separated points, and prove that there is no change from the 

 surface. 



The mica schists and gneisses are now considered by geolo- 

 gists to be shales and other clayey rocks of Hudson River (Lower 

 Silurian) age which have been altered to their present crystalline 



