November 30, 1888.] 



SCIENCE. 



255 



practical importance and value of pushing studies of the earth still 

 farther over all areas, and in greater detail. 



P'rom this it was seen that there vifould come additional isolated 

 pieces of information useful to the world, but especially the discov- 

 ery of general principles. 



Thus arose exploring expeditions ; and thus arose great govern- 

 ment surveys and international surveys, — surveys organized and 

 conducted systematically to study a great area, and to collect and 

 diffuse information for the benefit of the people. 



The general study of the earth as it has advanced has differen- 

 tiated itself into several special lines of study, and has been classi- 

 fied under six heads, as follows : — 



Geodetic Surveys. 



The primary object of a geodetic survey is the determination of 

 the size and shape of the earth, or, as is preferable to say in this 

 connection, the geoid. Secondarily and incidentally it accomplishes 

 much besides. It determines with highest precision the co-ordi- 

 nates, latitude, longitude, and altitude, of prominent land-marks 

 over the surface of a country. But this is not essential to its geo- 

 detic character. The earliest geodetic surveys by the French Gov- 

 ernment in France, Lapland, and I^eru, measured bases, executed 

 triangulation, and made astronomical observations, solely to deter- 

 mine the size and shape of the earth. 



If a scheme of triangulation were planned solely with reference 

 to the measurement of an arc of a parallel, or an arc of a meridian, 

 then the longest lines and the fewest stations and triangles con- 

 sistent with the required accuracy would be chosen. If the object 

 were the secondary one, of locating points upon which to base other 

 surveys, then the number, location, and accuracy of location would 

 be made dependent upon this secondary condition. 



The distinction here suggested is one not anywhere carried into 

 effect ; but by geodetic survey is usually understood a survey in 

 which long lines are measured with high precision, and are accom- 

 panied by astronomical and gravity determinations. Measures of 

 gravity, in so far as they contribute to a lyiowledge of the form of 

 the earth, naturally belong with geodetic surveys. In so far as they 

 relate to density and distribution of matter within the earth, they 

 form part of a geological survey. The methods and instruments 

 used, however, in the gravity, or gravimetric survey, closely ally it 

 to the geodetic survey, of which it properly forms a part. Thus a 

 geodetic survey will serve the double purpose of precisely deter- 

 mining the latitude, longitude, and altitude of points for practical 

 use, and of contributing to the general stock of knowledge respect- 

 ing the form, size, density, and distribution of matter of the earth. 

 And the conduct of the survey will vary according to the promi- 

 nence attached by the patrons of the survey to the one or the other 

 of these purposes. A very rigid adherence to the " practical " as- 

 pect of the case will lead to the rejection of all plans for work not 

 promising " practical " results, while a more liberal policy will go 

 further, and, in addition to the immediate practical results, will aim 

 to deduce general principles and increase the sum of human knovvl- 

 ledge. 



Geological Surveys. 



While geodetic surveys are concerned with the size and shape of 

 the earth, geological surveys deal with its structure, composition' 

 and history. The well-being of man is most intimately dependent 

 upon his power to forecast the future. To forecast the future re- 

 quires knowledge of general principles or laws, and these general 

 laws are derived by inference from what has been and is. To read 

 the story of the rocks aright ; to interpret their history ; to estab- 

 lish the principles, more enduring than the rocks themselves, by 

 which from that which has been may be correctly inferred that 

 which shall be, — this is the great geological problem not to be 

 solved by one geologist, or one survey, or one generation, but by 

 the accumulated results of the studies of many men, through many 

 generations. So conceived, it is clear that the work of the geodesist 

 and geologist will not be finished ; their work will not be perfect or 

 complete ; but each survey and each surveyor will do more or less 

 of good work or bad as his contribution to the world's knowledge. 

 The -greatest and best results of a geological investigation or sur- 

 vey may finally be summed up in the general principles deduced, — 

 principles capable of direct application to practical affairs. May 



wejnot hope some'day to understand volcanic and earthquake phe- 

 nomena, and, foreknowing destructive earthquakes, escape the 

 dreaded results .' 



The answer seems certainly to be worth the seeking ; and the 

 seeking must needs be made by studying the earth's crust. This 

 is the field of the geologist and the geological survey. 



The clay, the marble, the gold, the coal, the granite, the iron, — 

 these and many more in greater or less abundance, and very un- 

 evenly distributed, are useful to man. Are there not other unknown 

 natural products useful to man.' The geological surveys should 

 seek them. From the clay comes the porcelain and the bricks ; 

 from the marble, lime ; and from the coal and iron ore, the steel. 

 Are there not hidden from our view yet many more useful products ? 

 It seems highly probable, and therefore wise economy, that the 

 State should, for the common good, systematically collect, publish, 

 and distribute the data and information which render such discov- 

 eries possible. That the prosperity of a community depends upon 

 the amount and distribution of its natural resources is so obvious, 

 that the systematic study of them is early entered upon in most 

 civilized communities. Such systematic study is the first, the great- 

 est, and the most important work of a geological survey : it is the 

 foundation, and in many minds is conceived to be the only proper 

 work, of the survey. 



The purpose of a geological survey may be defined to be, to col- 

 lect, to systematically arrange, to publish, and to distribute, use- 

 ful information respecting the earth in general and its crust in par- 

 ticular. 



Respecting information not yet obtained, it may not be easy to 

 decide whether it be useful or useless. Is it of any use to know the 

 geological structure of the region about the north pole ? It may be 

 a frozen ocean, or a bleak, rocky region, fabulously rich in gold-de- 

 posits, or, — who knows? — perhaps a knowledge of so exceptional 

 a locality may furnish the key that will unlock unsuspected resources 

 at our very doors. A wise policy in the conduct of a geological 

 survey will ever seek useful information ; but a wiser one will add 

 to this search a deeper research into the unknown — far beyond 

 the limits of immediate pecuniary returns — for the discovery of 

 principles irrespective of immediate practical application. 



Topographic Surveys. 



The surface of the earth presents a great variety of forms and 

 features. Land is flat, undulating, broken, hilly, mountainous, 

 swampy, desert, etc. The free movement of men and traffic over 

 this uneven surface is much affected by its form : hence, for the 

 general information of those interested directly or indirectly in 

 travel or transportation, a knowledge of surface form is valuable. 

 Hence arise topographic surveys organized and carried on for the 

 purpose of collecting, publishing, and distributing information re- 

 specting the surface forms and features of a country ; i.e., respect- 

 ing its topography. 



' Topography ' is a word used sometimes in a broad sense to in- 

 dicate a description of a place or region not very large, and some- 

 times in a more restricted or technical sense to mean simply the 

 surface form, the ups and downs, the hills and hollows. In the 

 early use of the term, its meaning was the general, unrestricted one. 

 It is now used in both senses. If English catalogues of topograph- 

 ical books are examined, they will be found to consist of lists of 

 local town and county histories, local hand-books, guide-books, 

 gazetteers, accounts of noted buildings and persons, and of events 

 connected with local history. Maps or pictures may or may not 

 accompany such topographical descriptions. This is the early 

 English use of the word, — a use which still survives. 



Along with this early use of the word, large-scale maps of limited 

 areas were made, — maps which exhibited the hedgerows and high- 

 ways, the orchards and ditches, the parks and houses, the streams, 

 stone walls, gardens ; in brief, all the minor details of the land- 

 scape except the surface form. The features were exhibited usual- 

 ly by conventional signs, but the surface form was not revealed on 

 these maps. The horizontal plan alone appeared. The element of 

 relief was wanting. The scales of such maps, however, were so 

 large, that they permitted the exhibition of a large number of small 

 features ; and as such, they were called ' topographic ' in distinction 

 from • chorographic ' maps, which, on smaller scales, embraced in 



