INTRODUCTION

A mountain, a mesa, a cliff and, in fact, any major outcropping of rock normally has an accumulation of weathering products piled up around its base. Such an accumulation of rocks is commonly called talus. When these rocks are carried away from their site of origin by river or glacial transport, they become float deposits. As geologists, we prefer to collect our samples directly off the outcrop because we can precisely locate where on the outcrop they originated. If the outcrop is a steep cliff that we cannot climb, we may settle for a collection of rocks from the talus. Rocks collected from float deposits, however, may have been sorted during transport and may derive from many different sites along the path of the transporting agent. These contain the least information value and are generally ignored in favor of the other two sources. But suppose the original outcrop had been destroyed and its talus carried away, or for some reason was inaccessible? By now, geologists would have figured out all sorts of clever ways to extract information from the float about the inaccessible outcrop from which it came. This, of course, is the situation faced by meteoriticists: a meteorite is a sample of the detritus from an outcrop that either is inaccessible to us, or that no longer exists.