Geologists familiar with the formations of both hemispheres will in general agree that while Europe must always serve as the type region for the Mesozoic and Cenozoic formations, the North American Paleozoic should be considered the standard by which other deposits of that age must be judged. In no other known region is there such an extensive development of the older formations, both in their marine and continental phases, and in no other known portion of the world is the record so clearly preserved as in the Paleozoic rocks of the greater part of the North American continent. This is especially true of the earlier systems, which have not only a slight representation over much of Europe, but are for the most part strongly disturbed; or, where not so affected, as in the Russian region, are in large part covered by comparatively recent surface deposits. This is emphasized by . . .