2 72 % THE POPULAR SCIENCE MONTHLY. 



Eozoic scenery as a whole ; while an artist would find material for 

 only gne sketch. At the first we must conceive of an earth with a 

 larger diameter than is now accepted as the standard for the metric 

 system of measures ; of a shallow ocean covering the greater portion 

 of the surface, interspersed with numerous islands, scattered every- 

 where without any method of arrangement that' we understand. In 

 the areas marked as Eozoic upon our maps, accumulations of strata 

 were going on, of enormous thickness. We cannot recognize now 

 the original land which supported the primeval vegetation, but can 

 conjecture the boundaries of the contiguous oceans. In the latter 

 part of the period the areas of deposition occupied basins situated 

 within the limits of the earlier-formed rocks, being usually the deeper 

 portions of the original oceans. Ridges between the water-basins 

 resulted from the slow elevation of the land, the nuclei of great 

 mountain-ranges, and there were ejections of melted matter, with 

 marvelous alterations of sediments deep down beneath the surface. 



Respecting the age as a whole, we may say that the waters were 

 probably somewhat thermal, still simmering from the proximity of 

 the heated interior ; the air was thick and moist, partly composed of 

 carbonic-acid gas ; the sky was filled with dense clouds, marking the 

 transition of day and night by periods of total darkness and seasons 

 of feeble illumination, not permitting sunshine to cheer the vegeta- 

 tion. The life was characterized by its lowness of grade ; the terres- 

 trial plants hardly suitable for the food of air-breathing animals ; the 

 marine largely of the lime-secreting varieties and unicellular diatoms. 

 The animals colonized the bottoms of the oceans, building up enor- 

 mous reefs, but invisible to sight, if any one could have been per- 

 mitted to look upon the infant world. 



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THEORIES OF PRIMITIVE MARRIAGE. 1 



By HERBERT SPENCER. 



IN his ingenious and interesting work on "Primitive Marriage," 

 the words " exogamy " and " endogamy " are used by Mr. 

 McLennan to distinguish the two practices of taking to wife women 

 belonging to other tribes, and taking to wife women belonging to the 

 same tribe. As explained in his preface, his attention was drawn to 

 these diverse customs by an inquiry into "the meaning and origin of 

 the form of capture in marriage ceremonies;" an inquiry which led 

 him to a general theory of early sexual relations. The following out- 



1 From advance-sheets of Spencer's " Principles of Sociology," Part "The Domestic 

 Relations," chap, iv., " Exogamy and Endogamy." 



