Claire Shard., Age 14, Of St. Catharines, Ont.,Canada, for her question:

Are there really sea horses?

There are no handsome palominos, noble thoroughbreds or rebellious mavericks living in the sea. But there are ocean dwe11ers ca11ed sea horses. They are small fellows, dust a few inches long. They look somewhat me the horse on a chess board and just a little like the old gray mare.  The tiny head of the sea horse is like a caricature of a big horse who lives on land. The little fellow’s neck has the gracefal look of the real horse. But 1nstead Of legs and hoofs, he has fairy fins. He breathes through fishy gills, and his body is covered with scaly plates.  Susan Mitchell, Age G, Of Peterboro, Ont., Canada, for her question: What is the pre cambrian shield? The rocky layers of the earth's crust are like the pages of a diary. Limestone was built under the sea. Lava was poured from ancient volcanoes. Fine marble and heavy gneiss are rocks that have been remade from limestone and granite. The events of the earth's long long life story are written in this crusty diary.

A knight in armor carried a sword and wore a shield of metal on his arm. The Shield might be round or oval or some other shape. But it would be curved in a hump To fit on the arm of the knight. Geologists found a vast hump of hard, old rocks in North America, and because it was shield. shaped they called it a shield. It may be called the canadian shield or the pre cambrian shield. Later, humps Of such ancient rocks were found near the surface in other lands. All the continents, it seems, rest on pre cambrian shields of dense arid ancient rocks. This layer of sturdy rock is six to 10 miles thick. In same places it is 10 miles or more below the surface of the ground. In other places, it pokes up to the surface. Our world has had more than 4 billion birthdays, and all this time it has been Building a crust of rocky minerals, layer upon layer. The cambrian period of earth's history began more than 500 million years ago. The pre cambrian rocks were built before the cambrian period, starting 2 billion years ago. When they were new. The pre cambrian layers were made of shale and sandstone, lava and limestone. But in time these minerals were buried, crushed and remade by the terrific heat and weight from newer layers of rock. They became hard slate and heavy schist, dense gneiss and fine marble.

While new layers were being added, other events were going on in the crust of the Earth. Mountains grew and crusty layers were pushed up in folded wrinkles. The Pre cambrian rocks rose above sea level. Then the mountains were worn flat by wind and water. The top layers of the crust were washed away. The hard, pre cambrian shield was left at the top of the earth's crust.

The pre cambrian shield of North America is centered around Hudson Bay. It spreads east from the great lakes to Greenland and northern Europe. Some 2 billion years ago, this vast area was a massive mountain system. Ages of weathering have long sliced from arid leveled the ancient hills. Other shield layers; were ra7.bed and stripped bare in Asia and Europe.