150 



satisfactory basis, concurrently with or subsequent to the field 

 determination of the true relative positions of a number of 

 points in the several districts. 



6. Former triangulation useless. — This assertion, even if 

 established, in no way detracts from the advantages of a 

 trigonometrical survey honestly done, and reliable as a basis 

 of detail operations. Nor is there anything in the nature of 

 such a survey to make it a matter of uncertainty or speculation. 

 If funds are forthcoming, the result ought not to be pro- 

 blematical. 



7. Field inspection. — It would be interesting to learn what 

 extent of surveys were rejected or condemned " in the 

 days of field inspection." As the " severest tests " recognised 

 a limit of error of 32 links in the mile, the standard of 

 accuracy can hardly be considered high. To keep within the 

 limit specified was one of the conditions of each surveyor's 

 work, and it is obvious, therefore, that only those surveys 

 which were found on traverse inspection to exceed this limit 

 could be condemned. But, further, as there was no triangu- 

 lation by which to test the surveys on inspection, the in- 

 spector's own work would have to be discounted somewhat, 

 and allowing that officer a limit of error of 8 or 10 links in 

 the mile, as it would only be a traverse inspection, it is not 

 beyond the bounds of possibility to assume that he might 

 pass work which was erroneous to the extent of something 

 like 40 links in the mile, or 4in. in every chain. 



Apart from general considerations as to the wisdom and 

 propriety of establishing an accurate system of survey, the 

 fact that under the Real Property Act titles are issued for 

 certain pieces of lands, the boundaries whereof are defined in 

 the certificates and guaranteed, renders it not only desirable 

 but essential that the methods of survey and of record should 

 be such as to effectually guard against overlaps of boundaries 

 and consequent future claims and litigation. 



A DESCRIPTION OF THE REMAINS OF TRILOBITES 

 FROM THE LOWER SILURIAN ROCKS OF THE 

 MERSEY RIVER DISTRICT, TASMANIA. 



By R. Etheeidge, Jun., F.Gr.S, (of the Museum of 

 Natural History, London.) 



IBead ISth June, 1882.] 



I am indebted to the kindness of Mr. T. Stephens, M.A., 

 F.G.S., for an opportunity of examiaing the fossils which form 



