METHODS — GEOLOGICAL 9 



simple geometrical method from the surface exposiires of the 

 beds, such as mining engineers continually employ to map the 

 underground extension of economically important rocks, and 

 shows how an enormous thickness of strata may be studied 

 from the surface. The older beds are exposed at the western 

 end of the section in Wales and, passing eastward, successively 

 later and later beds are encountered, the newest appearing at 

 the eastern end. Very many of the strata are richly fossiliferous, 

 and thus a long succession of fossils was obtained in the order 

 of their appearance, and this order has been found to hold good, 

 not only in England, but throughout the world. The order 



Shlch of^Suecefiioti of STRjiT/i arui tJutr-nliLtive^ltLladis. 



Pig. 2. — William Smith's section across the south of England. The vertical scale is 



exaggerated, which makes the inclination of the beds appear too steep. 



N. B. The origiDal drawing is in colors, which are not indicated by the dotted strata. 



of succession of the fossils was thus in the first instance actually 

 ascertained from the succession of the strata in which they are 

 found and has been verified in innumerable sections in many 

 lands and is thus a matter of observed and verifiable fact, not 

 merely a postulate or working hypothesis. Once ascertained, 

 however, the order of succession of living things upon the earth 

 may be then employed as an independent and indispensable 

 means of geologically dating the rocks in which they occur. 

 This is the palceontological method, which finds analogies in 

 many other branches of learned inquiry. The student of 

 manuscripts discovers that there is a development, or regular 

 series of successive changes, in handwriting, and from the hand- 

 writing alone can make a very close approximation to the date 

 of a manuscript. The order in which those changes came about 



