Geology has long been the handmaid of Engineering. Instances are numerous in which the practical bearing of facts discovered by the devotee of the one have been recognized and utilized by the other. On the other hand, engineering enterprise has often put geologists in possession of facts of the greatest value as bases for fresh inductions. The subject now brought forward may perhaps sooner, or in a remote future, furnish another instance in which knowledge gained by the geologist may become available for a great economic purpose.