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wards ; but its limits are unknown. Scotland 

 presents one example, in which an uninterrupted 

 series of one rock, in a position approaching to 

 the horizontal, is nearly 4000 feet in depth. This 

 is the mountain Kea cloch in Rosshire, composed 

 of red sandstone. 



When the inclination is considerable, access 

 is obtained in a horizontal direction to a much 

 greater extent of a series ; and, in such cases, the 

 thickness of a collection of strata has been found 

 to amount to many miles. In Argyllshire the 

 lateral thickness of that which I have elsewhere 

 called the chlorite series, is nearly twenty. 



Strata are separated from each other by mathe- 

 matical planes, sometimes, (technically,) called 

 seams. They are also at times further divided at 

 some angle to their planes by other planes called 

 joints. In some instances, such joints are ob- 

 served to be parallel to each other. 



^series of strata sometimes consists of one sub- 

 stance, or rock, only ; at others, one prevailing 

 rock is divided by much thinner strata of ano- 

 ther ; as sandstone is by shale. 



