STRATIFIED ROCKS. 



191 



whole was again raised above sea and exposed to the in- 

 spection of the geologist ; the phenomena which would 







00 O 000 



FIG. 108. Some cases of unconformity. 



be observed are represented by Fig. 108, A, B, C. This 

 is what is called unconformity. More commonly in such 

 cases there is a want of parallelism between the two series 

 of strata, as in Fig. 108, A, B. But this is not necessary. 

 Fig. 108, C, represents unconformity no less than A and B. 

 In the one case the strata were raised into land-surface 

 and at the same time folded and tilted, and then eroded ; 

 in the other case, they were raised and eroded without 

 folding or tilting. Sometimes the second raising is also 

 attended with tilting, in which case both series are tilted, 

 but in different degrees, as in D. 



Definition. After this explanation, we are prepared 

 to define. When a series of strata are parallel, as if 

 formed continuously under similar conditions, they are 



