42 
ELEMENTS OF GEOLOGY. 
irregularities. We may sometimes follow a bed of lime¬ 
stone, shale, or sandstone, for a distance of many hundred 
yards continuously; but we generally find at length that 
each individual stratum thins out, and allows the beds which 
were previously above and below it to meet. If the materi¬ 
als are coarse, as in grits and conglomerates, the same beds 
can rarely be traced many yards without varying in size, and 
often coming to an end abruptly. (See Fig. 2.) 
Diagonal or Cross Stratification. —There is also another phe¬ 
nomenon of frequent occurrence. We find a series of larger 
strata, each of which is composed of a number of minor lay¬ 
ers placed obliquely to the general planes of stratification. 
To this diagonal arrangement the name of false or cross 
bedding” has been given. Thus in the annexed section 
(Fig. 3) we see seven or eight large beds of loose sand, yel¬ 
low and brown, and the lines a, c mark some of the princi¬ 
pal planes of stratification, which are nearly horizontal. But 
the greater part of the subordinate laminae do not conform 
to these planes, but have often a steep slope, the inclination 
Fig. 3. 
Sectiou of sand at Sandy Hill, near Biggleswade, Bedfordshire. 
Height 20 ft. (Green-sand formation.) 
being sometimes towards opposite points of the compass. 
When the sand is loose and incoherent, as in the case here 
represented, the deviation from parallelism of the slanting 
laminae can not possibly be accounted for by any re-arrange¬ 
ment of the particles acquired during the consolidation of 
the rock. In what manner, then, can such irregularities be 
