SEDIMENTARY AND METAMORPHIC ROCKS T7 
pebble or gravel 
beds; and when 
these are consoli- 
dated into a hard 
rock, they become 
what is known 
as a conglomer- 
ate (Figs. 26 and 
29). Between the 
rounded pebbles 
Fic. 28. 
A pebble beach, Cape Ann, Mass. 
there is usually a matrix of sand, and the large and 
Fig. 29. 
A conglomerate rock. 
small fragments are 
bound together by 
some kind of cement 
which consolidates 
the rock. There 
may be a very de- 
cided difference in 
the size and kinds 
of the pebbles, and 
there are limestone 
conglomerates, shell 
conglomerates  (co- 
guna) (Fig. 30), 
quartz-pebble con- 
glomerates, granite- 
pebble conglomer- 
