238 Correspondence — Mr. R. LydeMer. 



of the lateral digits of the fore-foot of an Artiodactyle Ungulate 

 allied to the Hippopotamus. The genus Drommis must therefor© 

 be expunged from the Siwalik fauna. 



I regret having made this unfortunate misidentification ; but am 

 glad to take this early opportunity of correcting it. A note to the 

 same effect will appear in the Introduction to the volume of the 

 " Palgeontologia Indica," quoted above, on its completion. 



E. Lydekkeb. 



SFBTERRANEAN CONTOURING ON GEOLOGICAL MAPS. 



SiK, — The notice in your March number, by my friend Professor 

 Benjamin Smith Lyman, of Northampton, Mass., regarding this 

 means of expressing the underground configuration of stratified 

 deposits would, I venture to think, have attracted wider attention if 

 it had dealt as fully with the manner of construction as it does with 

 the results to be gained. 



A long acquaintance with Professor Lyman's own use of this 

 system in the number of beautifully constructed maps which he has 

 produced of Japanese and other geological regions must be my 

 excuse for pointing out that, while the employment of the system on 

 a large scale by another American geologist (in the Pennsylvania 

 anthracite coalfield) is certainly evidence in his favour, the important 

 circumstances stated in the second sentence quoted from Mr. 

 Ashburner's report have an essential bearing upon the usefulness of 

 these contour lines. The quotation reads thus : — " The data which 

 are available for the construction of these maps are very extensive 

 and very accurate." This beings so, few will doubt that in such a 

 case plans showing true underground contours of coal beds, etc., 

 would be most valuable charts for the guidance of all kinds of 

 mining operations. But granting this involves the consequence that, 

 where the data are neither extensive nor accurate, the results will be 

 hypothetical and may be even largely based upon the safety of 

 assertions which there is no evidence to contravene, albeit there may 

 still be ample room for doubt. 



The forms and curvatures assumed by contorted strata varying 

 infinitely, it seems to me we may speculate ujDon, but cannot predict, 

 the continuity of any conditions at depths beyond the reach of direct 

 observation. We may trace an ellipsoid formed at the surface by 

 the outcrop of a synclinal basin, but without further information we 

 can scarcely foretell whether the interior rocks are, or are not, folded 

 again and again into anticlinal and synclinal curves, overfolded or 

 faulted, thinned away or crushed out. 



If what we call contortions had as uniform proportions as basins, 

 saucers, spoons or even casks, from any section of which some- 

 thing might be presumed regarding the size and shape of other 

 portions concealed, the theory of these contour lines would be 

 complete ; but as neither the shape nor size of a contortion has 

 relation to any standard, I do not see the advisability of laying down 

 upon ordinary geological maps, with the semblance of accuracy, what 



