240 Correspondence — Mr. T. V. Holmes. 



meaning and what is the classificatory value of these exterior bodies, 

 which I find also in the mud filling up the calices ? As soon as 

 time will permit, and drawings can be made, I will trouble you with 

 my views on these questions. P. Maktin Duncan. 



THE COMPLETION OF THE ONE-INCH MAP OF THE GEOLOGICAL 

 SUEVEY OF ENGLAND AND WALES. 



Sir, — An interesting article on the above subject appeared in the 

 " Times " of February 15th, and was reprinted in " Nature " of the 

 following week. No fault can be found with its general accuracy, 

 but I shall be glad to be allowed to say a few words on some 

 omissions that deserve notice. 



It is obvious that the goodness of a geological map depends 

 largely on the accuracy of the Ordnance Map on which the geology 

 is placed. No mention, however, is made in the above article of the 

 fact that the one-inch Ordnance Map of England and Wales is a 

 work of various periods and of men with very variable standards 

 of accuracy. Now the six northern counties had accurate six-inch 

 and one-inch maps when the geological survey was begun in them, 

 and their geology has been worked-out on the six-inch maps and 

 thence transferred to the one-inch maps. But in the southern counties 

 the geological work has been done on old and inaccurate one-inch 

 maps. Every year new and accurate six-inch and one-inch Ordnance 

 Maps of the counties around London are published, yet there is no 

 allusion in the "Times" article to the desirability of having the 

 geology of the district put upon these new maps. Should any one 

 think this work unnecessary, let him test the matter himself by 

 trying to transfer the geology of some part of Kent or Surrey from 

 the old Ordnance Maps, on which it now appears, to one of the new 

 sheets, and he will soon find he has undertaken an imjDossible task, 

 and be convinced of the necessity of a resurvey on accurate maps. 

 And as regards the completion of the survey of the superficial 

 deposits, mentioned in the " Times" as one of the things remaining to 

 be done, it is obvious that to do this on old one-inch Ordnance Maps 

 would be simply to waste the time of the Geological Surveyors and 

 the money of the public. Of course it may or may not pay to 

 jDublish six-inch geological maps of any given area, but the ad- 

 vantages of working on maps of that scale are enormous (even when 

 the production of one-inch maps is the sole object in view) both as 

 regards the amount and the accuracy of information displaj^ed on 

 the latter. When the whole of England and Wales shall have been 

 geologically surveyed on the six-inch scale, and the result transferred 

 to accurate one-inch maps, the duties of the Geological Survey of 

 that part of the United Kingdom will consist simply in keeping the 

 maps up to date — but not till then. T, V. Holmes. 



28, Cbooms Hill, Greenwich. 



