Many aspects of the seafloor-spreading hypothesis are bewildering. How can some midocean ridges spread symmetrically, yet others be shifted away from the block which the ridge material originally was spreading? How can a continuously spreading seafloor in the Pacific be concentrated into a smaller and smaller area (near the Marianas) without deformation? How can the "youngest" magnetic anomalies be closest to the Aleutian Trench? How can the Red Sea be spreading parallel with its topographic axis, whereas the magnetic anomalies strike obliquely to that axis? How do alleged anomalies beneath the 100–150 m.y.-old seafloors explain the history of events on continents, which are more than 3.5 billion years old? The seafloor-spreading hypothesis fails to explain many modern orogenic belts; how can it be utilized to explain older belts, especially those within continents? How does the hypothesis explain vertical movements—not just at continental margins but in continental interiors? It is my opinion that a hypothesis of vertical processes explains more satisfactorily the processes observed on continents. Can the two different hypotheses coexist? I doubt it. I believe that a truly global hypothesis cannot ignore the facts of continental geology—and seafloor spreading certainly ignores these facts.
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Plate Tectonics—Assessments and Reassessments
The general theme of this publication is the assessment and reassessment of various data, observations, and ideas about the earth as they relate to the concept that has come to be known as plate tectonics. Much widely scattered material was brought together for this publication, and its 24 papers contain an abundance of worldwide references that are important in studying plate tectonics.