There are few lines of investigation in geology which promise more fruitful returns than the lithogenesis of the sediments. The sedimentary rocks have from the first been sadly neglected although the igneous and metamorphic groups have been systematically and more or less intensively studied both in the field and in the laboratory. Even the megascopic characters of the sediments have for the most part been indefinitely and vaguely described and petrographic examinations have until recently rarely been made. Descriptive terms have been indiscriminately used and such important features as mud cracks and many others equally as significant have in many cases been wholly overlooked. Moreover, until within the last ten years few serious attempts were made to determine the conditions of deposition of the clastic sediments. It is little wonder then that the application of more refined methods of study to these rocks bids fair to revolutionize the fields of physical stratigraphy and paleogeography
