,HA. hll- AND nlTCKOP I09 



cntly ttut it can be satUfactorily traced from point to 

 for a long distant trat {graphically terviceable 



bands may be found in most districts of stratified rocks. 

 Great assistance in the tracing of horizons is likewise 

 afforded by organic remains, as has been already pointed 

 out A (articular stratum, even when ihin and other- 

 wise of no apparent importance, may acquire a high 

 value if it i> barged with fossils, and can be recognised 



a wide area. 



The outcrop may be marked at any particular locality 

 by a short line beside the di|Hurow, or if the outcrop be 

 a broad one, by two lines, one marking the base, the 

 other the top of the band. The space between two such 

 lines in other words, the breadth of the outcrop is 

 i by the thickness of the bed or beds, their 

 angle of inclination, and the slope or contour of the 

 ground. Amuiu' a series of vertical strata the breadth 

 of the outcrop of a bed corresponds exactly with the 

 .ijickness of that bed The more the angle of 

 inclination lessens, the broader does the outcrop at the 

 surface become. Hence, in tracing such a band across 

 a country, attention must constantly be given to the 

 variations of angle in the di; the dip increases 



the band narrows in breadth; where the : ; lessens the 

 hand widens. This is best seen on level or gently undu- 

 ground ; it is apt to be less distinctly shown where 

 the ground is . - n, and where therefore constant 



modifications of the line of outcrop are produced, as we 

 have seen to be the case with horizontal strata. When 

 strata are vertical no amount of surface irregularity 

 makes any difference on the width or direction of their 



