
are intermingled in beds of irregular thickness & lithological character as in unaltered mixed strata of the same nature. Most of them are exceedingly hard. They are continuously exposed in several directions to thickness of 6000 feet or more but the average breadth of the waves is not less than 5000 feet. 
The lines of stratification are distinctly marked. Above these slates & conformable with them, in a few localities mostly much elevated or on the western edge of the Island, are some of the Unga sandstone of the lower series. These are to be seen above