GRAVEL AND SHINGLE 301 
Specimens of Conglomerate are not difficult ‘to obtain in 
some localities—though typical varieties may not be so 
easily procured. 
Examine the specimens available and ascertain that they 
consist of bits of rock, often of different colour, shape and 
hardness (i.¢., the pebbles themselves belong to different 
rocks) imbedded or set in a cement or matrix. The whole 
looks like a plum-pudding with stones appearing through it 
instead of plums—hence the popular name, pudding- 
stone. Scrape away some of the matrix and detach a few 
of the pebbles. Notice that they are rounded and smooth. 
Educe that they are waterworn, and have been formed 
along a sea-shore or in a river-bed. 
Examine the matrix, 7.¢., remove some of this with a 
knife or hammer, and break it up either by rubbing it 
between the fingers or by gentle blows of a hammer, using 
no more force than is necessary to separate the particles. 
Place the powdered material ina glass jar containing water, 
shake up, and allow the jar to stand for some time until the 
contents begin to settle. If the matrix be composed 
entirely of sand, the particles will quickly drop to the 
bottom ; if of sand and mud, the sand will settle in a layer 
and the mud will remain suspended for a relatively long 
time. Determine in this way the composition of the 
matrix. 
Origin of Conglomerate. duce that the pebbles 
came from a sea-beach or river-bed—referring to any 
deposit of Gravel or Shingle in the neighbourhood. 
Refer to the way Concrete is made, viz, by mixing 
pebbles with slaked lime or cement and water, and leaving 
the mass to set. Educe that Nature in a similar way binds 
the pebbles and sand together partly by pressure and partly 
by causing some cementing material to find its way into 
the mass. 
