6oo THE POPULAR SCIENCE MONTHLY 



coral reefs occurring in Arctic regions, the sponge, coral and bryozoa 

 reefs in the Jurassic of northern Europe, the rudistid and other 

 cemented pelecypods in reefs of wide distribution in the Cretaceous, 

 and the almost world-wide distribution of the Nummulitidae (north of 

 Siberia) in the late Eocene and Oligocene point as clearly to warm 

 waters and mild polar climates. Further the widely distributed Car- 

 bonic foraminifers of the family Fusulinidse that swarmed in temper- 

 ate and tropical regions are unknown to Arctic and Antarctic regions. 

 In other words, long before we have a fossil record the earth had cli- 

 matic zones, and for long periods the climate was mild to warm, 

 punctuated by shorter intervals of cold to mild climates. 



The volume of sea water to-day is very great, but we must ask our- 

 selves: Has this quantity always been such or was it even greater, as 

 some geologists still hold? We no longer agree with Laplace and 

 Dana that the earth passed through an astral stage, but rather agree 

 with Chamberlin that it always has had a more or less cold exterior. 

 Through volcanic activity much juvenile water from the interior of the 

 earth was extruded in geologic time and was added to the vadose waters 

 of the surface. Suess states that " the body of the earth has given forth 

 its oceans and is in the middle phase of its gas liberations." Accord- 

 ingly, the Paleozoic oceans must have been quantitatively smaller than 

 those of the present, and the gradual increase in the volume of vadose 

 waters has been accommodated by the periodic increase of oceanic 

 depth. 



We also agree with Walther that the oceans of Paleozoic and earlier 

 time did not have the great abyssal depths they now have. The ac- 

 centuated deepening of the permanent oceanic basins did not begin 

 until the Triassic, for in none of the great depths of the present oceans 

 are found traces of Paleozoic organisms, and all here are of Mesozoic 

 or Tertiary origin. In the shallow regions, however, are still found 

 a few Paleozoic testaceous-bearing genera of brachiopods, tubicular 

 annelids, pelecypods, gastropods, Nautilus, and Limulus. The deepen- 

 ing of the Pacific, the Indian, and especially the Atlantic oceans has 

 been at the expense of the lands or horsts, for the ancient continents, 

 Gondwana and Laurentia, have each towards the close of the Mesozoic 

 been broken into several masses. We may therefore speak of permanent 

 oceans, and transgressed, fractured, and partially down faulted, con- 

 tinents or horsts. 



These are some of the factors that control the making of some of 

 the modern paleogeographic maps. 



