58 
STRATIFICATION. 
sisling of one substance only, but that there are 
various kinds of substances, such as soil, sands, 
gravels, clays, limestones, slates, granite, &c., min- 
gled together, perhaps, in apparent confusion, but 
still presenting appearances which often interest 
even the most ignorant observer. How interesting is 
it to find, on more extended examination, that these 
apparently confused masses are arranged in a regu- 
lar order of succession, and that a slight acquaint- 
ance with geological facts and principles furnishes 
a clew to unravel, as it were, the intricate web of a 
world's formation ! What advantage, too, does the 
geologist possess over those whose observation is 
not guided by the principles of science. He alone 
knows where we may expect to find valuable min- 
erals, such as coal, iron, salt, gold, silver, lead, &c. ; 
and millions of dollars might have been saved in 
searching for these hidden treasures had those en- 
gaged in the pursuit been acquainted with the merest 
elements of the science. 
Rocks have been divided into stratified and un- 
stratified. Stratified rocks are those which are di- 
vided into beds parallel to each other, or which, 
though not parallel, are arranged in separate layers. 
Various disturbing causes may have destroyed the 
parallelism of these beds ; still the term is retained, 
and the beds are called strata. Indeed, it is a very 
rare thing for the layers to be perfectly parallel or 
horizontal, as the disturbing forces have deranged 
their position, and thrown some above, while others 
remain depressed below the general level. 
Strata are said to be horizontal when they have 
no inclination with the horizon, thus ; 
Fig. 9. 
