124 



OfTI.IM S ol I II I.D-C.EOLOGY 



PART 1 



succession of n<ks and need not mark any bivak in 

 the geological sequence. Conglomerate! have often 



kii^t^Si^-^'A^l ' K '<-' n a>suined to IK- proofs \ uncoil 

 formability. Unquestionably they 

 frequently occur at an unconformable 

 junction ; but they appear also in the 

 midst of the most perfectly < on: 

 able strata, as may be illustrated by 

 'iong the Palaeozoic 

 rocks of Hritain. In Fig. 33, for 

 example, a section is given of about 

 1500 feet of the Lower Old 

 Sandstone in Midlothian. It will be 

 seen that high above the massive 

 bottom conglomerate other coarse 

 conglomerates occur at different 

 FIG. 33. Section of a por- horizons in an entirely conformable 



tion of the Lower Old 



Red Sandstone, Pent- succession of strata hundreds of feet 

 land Hiiu ,/, Upper above the base. 



In ttlOSt CaSCS it is possible SO tO 



P " unconformable junction 

 upon the map as to make it readily 

 apparent to the geologist It should be the aim of the 

 surveyor to neglect no item of evidence which will 

 enable him to do this ; for the more perfectly his 

 map is self- interpreting, the more useful will it be. 

 Hence where, as is often the case, the ground is 

 obscured by surface -accumulations, and a little liberty 

 of choice is left to him as to the precise course along 

 which to place his line of unconformability, he will 

 draw this line in such a way as to show as clearly as 



Silurian shale, covered 

 unconformablyby c,c,c, 



