Palæontologists and others concerned with fossils often X have need of some method of taking impressions of fossils, which shall at the same time be simple and efficacious, and shall also be of such a nature as not to cause injury of any kind to the original. Many different processes have been tried, with varied success. The following method has stood the test of application to a wide range of subjects, and has answered its purpose well in the hands of a considerable number of workers:—