28 
POPULAK SCIENCE EEVIEW. 
comfited. There was nothing for it but to advertise ; so we 
wrote out several large bills describing the maps, and offering a 
reward for their return, which we placed in the village shops. 
Two days passed in suspense ; then, on the evening of the third, 
a farmer came in with them. He had found the map-case on 
the gate-post, and had put it into his pocket and taken it 
home ; but here he did not stop ; he gave it to his little child 
to amuse itself with ! Happily the maps were all right, un- 
harmed, and we were thankful ; though a sort of thrill ran 
through us as we thought of our maps, with three months’ 
work upon them, as a plaything in the unscrupulous hands of 
a child ! So much for agricultural appreciation. Let us now 
turn our attention more seriously to the subject of geological 
maps. 
It is well known how our British rocks are mostly of the 
“ stratified ” kind — rocks deposited under water — such as slate 
and clay, limestone and marl, sandstone, sand, and conglome- 
rate, intercalated one with another, and occurring at all 
horizons in the earth’s crust, generally harder or more compact 
the older they are. It is also well known how these rocks are 
arranged in a certain regular series, characterised by peculiar 
mineral characters, and more particularly by assemblages of 
fossils which are more and more closely allied to the forms of 
life now in existence, the newer the rocks in which they are 
embedded. Thus we have the table of British strata, such as 
the old red sandstone, the lias, and the chalk ; the oldest rocks 
known being the Laurentian, the newest including the alluvial 
deposits of our present streams. This order of superposition 
is never inverted, except by local and extremely rare distur- 
bance, when the rocks may be folded or bent over so as to 
bring the older above the newer. We have also in England, 
though they occupy a comparatively small area, many “ un- 
stratified” rocks, the result of old igneous eruptions, and 
metamorphic rocks which in bygone times have lost their 
original stratified character through the agency of heat. These 
rocks include the toadstone of Derbyshire, and the granites of 
Cornwall. 
The arrangement of our stratified rocks has been aptly com- 
pared to layers of cloth of various colours and irregular shapes 
overlying and overlapping one another; some squeezed or 
rucked up with even layers deposited upon them, but yet 
arranged in a definite order comparable to that order of succes- 
sion into which all stratified rocks may be determined. Each 
layer may be taken to represent a series of limestones and 
clays, or sandstones and conglomerates, or slates. Some layers — 
the lowest ones, perhaps — may be rucked up into mounds higher 
than all the rest, and yet they are clearly the oldest, because 
