28o 



UNSTRATIFIED ROCKS 



Intrusive Sheets or Sills. — These are horizontal or moderately 

 inclined masses of igneous rock, which have small thickness as 

 compared with their lateral extent. Sheets conform to the bed- 

 ding planes of the strata, often running long distances between the 



FIG. 124. — Sheet of jointed diabase. Orange, N.J. (U. S. G. S.) 



same two beds ; but if they can be traced far enough, they may 

 generally be found cutting across the strata at one point or 

 another. In thickness they vary from a few feet to several hun- 

 dreds of feet. The Palisades of the Hudson are formed by a 

 sheet of unusual thickness ; its outcrop is 70 miles long from 



