Travel Reference
In-Depth Information
little formal schooling, found writing difficult and searched for another way
to illustrate his results. He hit upon the novel idea of publishing a map of ge-
ology, not geography. Each region of differently aged rock was accorded a dif-
ferent color on his map, a ptactice still in use today. Smith, in constructing
the first
geological map,
produced one of the first time machines, for his map-
ping of strata became one of the earliest and most accurate ways of studying
ancient time.
Smith's life's work, the first geological map of England, was published in
1815. It was a revolutionary document and, like many such advances, was
little noticed for many years. Smith himself received little recognition for his
discovery in his lifetime. Yet gradually word of this new tool did spread, and
by the second decade of the nineteenth century, many geologists began to re-
alize what Smith had long known: Rocks could he formed at any time in
earth history, but fossils could not. Limestone could be formed at any time,
but limestone containing ammonite fossils could be no younger than the
Mesozoic Era.
Here, then, was the new tool. You could not determine the actual age
of a rock, in the sense of age as we know it. Even with a fossil, you could
never identify a rock as being so many hundreds, or thousands, or millions of
years old, and indeed no societies of the time could make any accurate esti-
mate about how old the earth and its rocks were. But you
could
quite accu-
rately determine which rock was younger and which older, and this made it
possible to undetstand and map the structure of the earth's surface and, in so
doing, discover its underground secrets and mineral treasures.
The use of fossils as relative indicators of time was soon taken up by ge-
ologists all over the European continent. Major units of time were based on
the unique fossil assemblages that were characteristic of them. These subdi-
visions, though originally based on actual rock bodies, became de facto units
of time. For instance, an English geologist named Adam Sedgewick spent
several summers in the early part of the nineteenth century studying strata
found in Wales. These rocks showed the transition between lower strata de-
void of fossils and overlying strata filled with fossils—the transition we now
know to mark the start of the Paleozoic Era. Sedgewick named the fossilifer-
