7 o8 THE POPULAR SCIENCE MONTHLY. 



fer a very considerable retardation in their passage through space. 

 Encke's comet formerly came regularly back into the field of the 

 earth's orbit once in every three years, but with a period shortened 

 six hours each time. The whole planetary regions seem to be filled 

 with collections of matter star-dust and meteorites. They are all 

 revolving about the sun in eccentric orbits, and are doubtless slowly 

 circling toward it. The zodiacal light is supposed to be only an im- 

 mense aggregation of this material. Thus the thickening stratum as 

 these strange bodies draw near to the sun shows that they are all 

 slowly gathering to that great centre of attraction. 



The evident effect of the fall of any of the planets into the sun 

 would be the diffusion of highly-heated vapors far out into the spaces 

 that surround it probably far enough to reach the next outlying 

 planet, and thereby to increase its retardation and hasten its fall into 

 the mighty caldron. So one by one the planets dissolve and their ele- 

 ments fill the void of space. The expanding gases catch up the waves 

 of radiant heat that have long been wandering from planets and suns; 

 and the nebula is again seething and surging with its mighty contend- 

 ing forces. Sun-system reaches out to sun-system, and star-galaxy 

 mingles with star-galaxy, till through all the abysmal depths matter 

 is again " without form and void, and darkness is upon the face of the 

 deep." Chaos has returned once more, again to be breathed upon by 

 the Omnipotent Spirit that reforms and recreates. 



-- 



ACCOUTREMENT OF A FIELD-GEOLOGIST. 



By Professor GEIKIE, F. B. S., 



DIRECTOR OF THE GEOLOGICAL SURVEY OF SCOTLAND. 



FIELD-GEOLOGY does not mean and need not include the col- 

 lecting of specimens. Consequently a formidable series cf ham- 

 mers and chisels, a capacious wallet with stores of wrapping-paper 

 and pill-boxes, are not absolutely and always required. Rock-speci- 

 mens and fossils are best collected after the field-geologist has made 

 some progress with his examination of a district. He can then begin 

 to see what rocks really deserve to be illustrated by sj^ecimens, and 

 in what strata the search for fossils may be most advantageously con- 

 ducted. He may have to do the collecting himself, or he may be able 

 to employ a trained assistant, and direct him to the localities whence 

 specimens are to be taken. But, in the first instance, his own efforts 

 must be directed to the investigation of the geological structure of 

 the region. The specimens required for his purpose in the early 

 stages of his work do not involve much trouble. He can detach 

 them and carry them off as he goes, while he leaves the full collection 

 to be made afterward. 







