78 WALKS AND TALKS. 



complications. These are easily illustrated. Glue together 

 thin board-like pieces of pine, cherry, oak, beech, mahogany, 

 apple or other woods, to represent strata. Then cut the pile 

 in various slopes and curves, and notice where the various 

 sorts of wood outcrop. This represents precisely what we ob- 

 serve in the actual arrangements of outcrops. But the Drift 

 covers so much that we often experience difficulties in finding 

 where the rocky outcrops lie. 



The complications in the structural arrangements of the 

 rocks are still greater. Anticlinal dips pass off each side into 

 level strata or synclinal arrangements. A synclinal arrange- 

 ment is often along the highest region, instead of the lowest, 

 as one would expect. On the contrary, an anticlinal arrange- 

 ment is often along the bottom and sides of a valley, instead 

 of running along the crest of a mountain, as one might expect. 

 These things result from extensive erosions. Again, the dips 

 sometimes become very great even -vertical and there may 

 be difficulty in deciding which is the upper side of a stratum. 

 Worse than this, we sometimes find a pile of strata tilted so 

 far as to seem to dip in the opposite direction. Then the 

 older and lower strata in fact lie uppermost, and seem to be 

 newer. This inversion of strata sometimes occurs along the 

 Appalachians. 



But there are some compensations for all this confusion. 

 The Eozoic, or crystalline rocks are lowest of all in position, 

 and when they are in sight they form a landmark from which 

 we can estimate upward. Remember, however, that the low- 

 est rocks lowest in geological position are often highest in 

 topographical position. They are often at the summits of 

 mountains, as in the Alps and the Rocky Mountains. The 

 newer strata then slope down in order along each side of the 

 mountain, and pass under the plain. 



In the next place, strata are to some extent, arranged in 

 long folds, which here rise in a ridge, and there disappear un- 

 der a synclinal. Such long drawn forms are found along the 

 Laurentian hills in Canada, and along the Appalachians. 

 Here we catch sight of a general method in rock arrangements. 



