394 



SCIENCE. 



[Vol. I., No. 14. 



separated in regiud to animal distribution. This 

 latter point goes far toward being the sole cause of 

 regions. Any large mass of land separated from the 

 rest of the world will, in the course of time, become 

 inhabited by a peculiar set of animals, and obtain 

 a comparative balance or stability of life. Thus a 

 number of species are evolved which forms a sort of 

 compound whole, — the life of a region. So a region 

 may be defined as the area occupied by a peculiar 

 grouping of animals which are isolated from the life 

 of the rest of the world; the word 'peculiar' refer- 

 ring to the animals as a whole, and the isolation as of 

 a limited and not absolute degree. 



Accepting the above definition, the world can be 

 conceived of as divided into regions, which, if the 

 laud and sea remained at rest, would be jDermanent, 

 but constantly growing more and more distinct. But 

 the land is not permanent. While the main mass is 

 a fixture, minor changes occur, wliich join and sepa- 

 rate the continents. As soon as two lands are joined, 

 unless some other very powerful barrier exists, the 

 life of the two at once begins to blend. The more 

 potent kinds survive, while the weaker die out. The 

 first, together with the life modified by the new con- 

 ditions (new species evolved), in the course of time 

 form a single region. On the other liand, if a land 

 become divided into two, tlie reverse takes place, and 

 two regions are formed. To me the palearctio and 

 nearctic regions seem to oiier illustrations of both 

 these processes ; the connection for life having been 

 made and broken between tlie old and new worlds, 

 probably by means of Asia, more than once. At 

 present it is broken ; and the nearctic and pale- 

 arctio regions are formed or forming from a previous 

 circumpolar region. With the tentative definition 

 given here, the two are regions, since they do not 

 form a group, and are separated. No lack of percent- 

 age difierences can make the life of the two regions 

 closely related: a change in one does not necessitate 

 a change in the other. This also answers the circum- 

 polar question : the resemblance in zones is due, first, 

 to the imperfect obliteration of the old circumpolar 

 region; and, secondly, to the fact that some of the 

 forms which inhabited it have been driven down into 

 the southward-pointing peninsulas, where the condi- 

 tions of their life are easier. Accordhig to this defini- 

 tion, Madagascar should be regarded as the remains 

 of a fading region, rather than a part of the Ethio- 

 pian. The resemblance between Africa and India is 

 due to a southward migration wliich occurred not so 

 long ago, very likely on account of the ice age, from 

 a northern central i^oint. 



The above crude suggestions would seem sufficient 

 to show that regions are more than numerical rela- 

 tions, and have an evolution of their own. 



.J. Amory Jeffries. 



Panther Creeli coal-basin. 



I have just read your review of the Panther Creek 

 atlas, in Science, No. 11, and my attention has been 

 directed to what I consider a very just and proper 

 criticism of two special features of the atlas sheets : 1°. 

 The discordant scales of the mine (801)'= 1") and topo- 

 graphical ( 1(300' = 1") sheets. 2°. The use of the mag- 

 netic instead of the true meridian. As a geological 

 critic, I should be disposed to boldly condemn what 

 you have referred to as merely misfortunes. After 

 an association of nine years with Professor Lesley on 

 the Pennsylvania state survey, I am convinced, that, 

 in the successful conduct of such a survey, it is quite 

 impracticable to attempt to attain a purely technical 

 and systematic standard of work. All that can be 

 done is to approach as near as possible to such a 



standard, while meeting the practical demands for 

 geological results, to aid in the economical exploitation 

 of our mineral resources. This latter is what has 

 popularized the work of the Pennsylvania survey, 

 and accounts for its uninterrupted continuance with 

 liberal appropriations for a state survey, since 1874. 



The published results of the survey so far relate 

 mostly to topographical, geotectonic, and stratigraph- 

 ical geology in their economical bearings, with the 

 exception of two volumes on paleobotany. Had any 

 other plan than tliat of Professor Lesley's, which 

 he has so elBciently carried out, been instituted, 

 the survey would never have been so liberally sup- 

 ported by our state legislature, and probably would 

 have been discontinued several years ago. The im- 

 jjortant thing in a state survey is to do the best we 

 can. If we attempt too much, we fail in all. 



In regard to the discordant scales and magnetic 

 meridian, I would say: 1°. That the publication com- 

 mittee of the board of commissioners has never before 

 authorized the printing of general maps on a scale 

 larger than 1600'=1". This scale was found quite too 

 small for the anthracite-mine sheets, and it was only 

 after the most careful consideration on the part of the 

 committee that a scale of 800'=1" was adopted for 

 the mine sheets. The smaller scale was unfortunately 

 adhered to for the topographical sheets, on account 

 of the cost of publication. 2°. In the Panther Creek 

 basin, the magnetic meridian of 1809 is always used 

 in all surveys ; and the block-lines referred to this 

 meridian on the atlas sheets have been similarly 

 placed on all the large working mine maps. In this 

 form the sheets are of much greater practical value 

 for ready reference. Had the publication of this 

 atlas been delayed until the completion of the astro- 

 nomical determinations of the survey in this locality, 

 we should probably not have obtained an additional 

 appropriation to continue the survey, which we now 

 feel assured of receiving. 



Charles A. Ashburner, 



Geologist in charge. 



Philadelphia, April 21, 1883. 



Crayfish. 



In August, 1882, while in Fairmount Park, Phila- 

 delphia, I found a crayfish in a brook emptying into 

 the Wissahickon Creek. It had its under parts cov- 

 ered with young crayfish about one-eighth of an inch 

 long. 



Professor Huxley says that the English species, As- 

 tacus fluviatilis, lays eggs in May and June, and the 

 young leave the female in a few days; but the young 

 staid ten days with the female after I found them. 

 There seems to be a difference in their habits in this 

 respect. Last Friday, April 6, I found a fem,ale cray- 

 fish with young ones clinging to it, which I caught; 

 and a friend now has it in a tank. Do crayfish lay 

 eggs both early in tlie spring and late in the summer? 

 Richard M. Abbott. 



Trenton, N.J. 



[The writer of the above is eleven years of age. — ■ 

 Ed.] 



Marking geodetic stations. 



The writer of the article in Science of April 13, 

 1883, p. 269, in referring to the method of marking 

 tlie geodetic stations in the N. T. state survey, makes 

 the statement that the U. S. coast survey stations are 

 indicated 'by no surface-mark whatever,' trusting 

 entirely to the underground-mark for the preserva- 

 tion of the station. The writer has, doubtless, been 

 misled by visiting a station from which the surface- 

 marks have been removed by curious or malicious 

 persons. In the coast survey the greatest stress is 



