430 On the Government Trigonometrical Survey. 



well settled in the net-work of Lines) and the Stations on sur- 

 toundiiig Hills, might be selected, for making this series of ol" 

 served data, as to refraction, join to and blend with the lower 

 ones already obtained by Astronomers. 



" Fifth, Very carefully ascertaining the horizontal hearings, 

 or Azimuths, of the lines of Triangles, with the Meridian, at 

 everTj Station; which vet has been done at a few only, and at 

 fewer still, in a quite satisfactory manner. 



" Sixth, The difference of time, or longitude, to be deter- 

 mined, by often repeated signal-lights, made and observed at 

 the opposite ends of all such long lines of the Triangles, as have 

 nearly an E and W direction. For which last purpose, if two 

 exactly similar apparatus were provided, and simultaneouslyused, 

 in the Pendulum observations, mentioned in your last Letter, 

 the time or trouble of the same, might not be materially in- 

 creased, by combining these very important longitude observa- 

 tions. 



" Seventh, That the Strata, for a circle of three or four Miles 

 around each station, should be carefully surveyed and mapped, 

 in connection with Mr. Smith's Map of the Strata, which may 

 then sufficiently supply information, as to most of the interme- 

 diate parts of the Island's surface. 



" Eighth, That the direction and degree of the general dip 

 oj" the Strata, at each station, should be carefully ascertained, 

 and a vertical Section in that direction, made through the sta- 

 tion, of three or four Miles long on each side of the station, 

 either equally so or otherwise, and other cross Sections, in any 

 case where the Station proved to be on, or near to a ridged or 

 curved plane of strata (as is not very uncommon) ; thus showing 

 the actual thicknesses and forms, and describing the positions of 

 the several strata, as deep as could, without any material expense 

 of sinking on the bassets, be ascertained. 



" Ninth, That experiments on the specific gravities of Spe- 

 cimens of the Stones or Earths, &c. forming each distinct stra- 

 tum, shown in the Maps and Sections, collected at proper di- 

 stances below the surface, at several points in the course of each 

 stratum, should be made, on or near to the spot, before the drying 

 or partial dejomposing of such Sj)ecimens3 and that ample and 

 numerous duplicates of all such Specimens, should be labelled 

 and preserved, and deposited in the National Collection (by 

 Mr. Smith and others) for illustrating the British Strata, now 

 forming in the British Museum ; together with copies of the 

 Maps and Sections, having marked on them the exact site of 

 each of such Specimens. 



*^ No progress whatever has yet been made by the Trig. Sur- 

 veyors, 



