98 
THE GEOLOGIST. 
much. If the strata were spread out and piled up universally one over 
the other this would be the height of our knowledge ; but they are not 
so stacked nor are they concentrically enveloping. They are tilted up at 
various angles, and cutoff at their outcrops at the surface; great bent domes 
of rocks, once continuous over miles of country, have been carried wholly 
away, and their materials re-deposited in the abysses of the sea. More- 
over, tliese beds never were strictly horizontal except in a few cases ; 
they are generally the produce of the littoral and marginal areas 
of the prc-adamic oceans, and are most commonly wedge-shaped, thinning 
out ,or thickening, one beneath the other. Geologists do not dwell 
sufficiently upon tliis sea-marginal and inclined deposition of the rocks ; 
they are too careless and too ready in their use of the term "horizontal 
stratification." There is very rarely any such thing in nature, 
and this little fiict makes a great difference. Suppose ten strata, 
all inclined at the same angle, and each half-a-mile thick at its 
outcrop. 
LiGM. 11. — Strata of equal thicttnesa deposited at the same angle, and 
supposed to be continuous in their dip. 
By the argument of original horizontality it is evident we should — by 
walking over the country, and measuring the thickness or width of 
the beds at their bassetting edges, a\ a"^, a^, to «'» — allowing only for the 
angle of inclination in our measurements — acquire a knowledge of the 
nature and characters of these rocks equal to five miles in vertical depth 
at the point a". 
But these rocks were deposited with a diminishing or increasing 
