In the tradition of the old Ace Doubles (flip one book over to read the second), here's the twenty-third Wildside Double:
THE SPACE WARP: A SCIENCE FICTION NOVEL, by John Russell Fearn.
In Annex 10 in the Adirondack Mountains in New York, the scientists under the leadership of astronomer Dr. Gray can hardly believe the things their instruments are telling them; but, because their equipment is absolutely reliable, they HAVE to believe, and on that ill-fated June 30th, they begin to see the chaos will affect mankind. The Earth is growing steadily hotter. Temperatures rocket as the sun shines through the night and the world is plunged into endless day. Everywhere people are suffering--rich and poor, criminal and family man--and none know if or when relief will ever come. Is this the end of the world as we know it?
INTO THE UNKNOWN: A SCIENCE FICTION TALE, by John Russell Fearn.
A laboratory accident suddenly sends four modern-day humans backwards in time, their individual organic bodies almost untouched by the phenomenon, while the physical world around them gradually retreats through the ages. Onward and onward they careen through the past, until they appear in the vividly green Carboniferous Age, filled with overwhelmingly excessive vegetation, festering swamps, and fetid lagoons. The accumulation of rotted vegetation is everywhere around them, vegetation that will eventually become peat, and then through accumulating pressures and chemical change, hard black coal--coal for a future that has already been destroyed. Paradoxes of time--infinite and complete--surround them. But what can they actually do to save themselves...?