Duane Peterson, age 12, of Bronson, Iowa, for his question:

WHAT IS A GEOSYNCLINE?

This grand sounding word was invented in 1873. Geosyncline belongs to the geologists, though at first they had practically no use for it. Then, for a while, the word became very popular. Lately it has gone out of style, though .some earth scientists use it when describing the past history of the continents.

Early in the last century, almost everybody thought that the earth was no more than a few thousand years old. Then Louis Agassiz proved that massive glaciers crept over Europe a million years ago, but almost nobody believed him. When others found evidence that enormous ditches existed hundreds of millions of years ago, people had to admit that the earth must be very old  much older than just a few thousand years.

Geologists coined a new word to name these strange ditches in the earth's crust. They called them geosynclines and tried to figure out what happened to them.  For example ,during the Paleozoic Era there were two great geosynclines in North America. This long gone chapter of the earth's history began about 600 million years ago and lasted through perhaps 375 million years.

This was even before the days of the giant dinosaurs. There were no Appalachians along our Eastern shores and no proud mountains in the West. Instead of these familiar ranges there were two geosyncline ditches in the earth's crust.

Actually they were long and rather narrow hollows, filled or partly filled with water. Streams drained down the slopes on each side, carrying muddy silt and gravel. Through the ages, this dirty debris collected in the geosynclines. They filled up with soggy sediments, and their floors became heavy. Shells and other fishy fossils were buried in this new rocky material.

Some geologists suspect that the heavy sediments in the geosynclines caused great changes in the earth's crust. Perhaps this is why huge crustal slabs were pushed up to form mountains. In any case, before our Eastern and Western ranges were born, their places were occupied by shallow geosynclines.