This is a big, beautiful book!  It's well done, as all of the Usborne books that I've seen are.  We're reading it this year (98-99) for part of our science curriculum.  We're reading two pages a day which ends up giving us 43 days worth of science.  It's been sitting on our shelves for about two years; we've been using it as a reference book.  But I just figured that we could read it cover to cover since it's such a colorful and interesting book.  With every turn of the page, we are met with a plethora of illustrations.  I feel that this book is good for about 4th - 6th grades (as curriculum), while the Usborne catalog says that Natural World is appropriate of ages 10 and up (as a reference).

Here's the Contents:
How Plants Live
Plant Reproduction
Fruits and Seeds
Trees
Ferns, Mosses and Liverworts
Microscopic Life
Mushrooms and Toadstools and other Fungi
Worms
Snails, Slugs, Centipedes, Millipedes and Woodlice
Insects
Butterflies and Moths
Bees and Wasps
Ants and Termites
Spiders, Mites and Scorpions
Seahore Life
Fish
Sharks and Rays
Reptiles
Turles and Tortoises
Crocodiles and Alligators
Snakes and Lizards and the Tuatara
Frogs, Toads and Salamanders
Birds
Birds of the World
Mammals
Lions and Tigers and of Wild Cats
Wolves, Foxes and Wild Dogs
Weasels and Stoats and other Small Carnivores
Bears, Pandas and Raccoons
Whales and Dolphins
Seals and Sea Lions and other Sea Mammals
Monkeys and Apes and Small Primates
Elephats and Rhinos
Zebras, Hippos and Giraffes
Camels, Llamas and Wild Cattle
Wilde Sheep, Goats and Pigs
Deer
Antelopes
Rodents
Hares, Rabbits and Pikas
Moles, Hedgehogs and Shrews
Bats
Toothless Mammals
Horses and Donkeys
Farm Animals
Mammals of Autralia and South America
Ecology
Rivers and Lakes
Mountain Wildlife
Tropical Grasslands
Deserts
Tropical Rainforests
Polar Wildlife
Seas and Oceans
Wildlife in Danger
Evolution
Classification of the Natural World
Map of the World
Glossary
Index

While this isn't a "must have" book like the Kingfisher History Encyclopedia, I really like it and am glad that we're able to utilize it.