Application of Electro -Magnetism to Astronomical purposes. 51 



drift ; but the tertiary beds appear at the brick-kilns and Cla- 

 rendon Lodge_, and advance in importance as we proceed east- 

 war d^ so as to occupy all the country in which the words Alder- 

 bury^ Whitmarsh-bottom, Bentley Wood^ Berrywell Wood, and 

 French Moor are to be found. The chalk on which these tertiary 

 beds repose emerges at East Grinstead and West Dean, in a low 

 ridge dipping sharply north; whilst the opposite side of the 

 anticlinal consists in the strongly-marked feature of Dean Hill* 

 dipping southerly. Grimstead Fields is a chalk saddle between 

 these two ridges. Still proceeding eastward, the northern ridge 

 is gradually intruded upon by the plastic clay, and is lost under 

 it at Lockerly. The southern, in the line of Dean Hill, still 

 maintains its importance ; but that also slopes away to the south- 

 east, and is soon covered up by tertiary formations : Mount 

 Farm, Butler's Wood, Uphill, Roke, are tertiary or shingle beds 

 of the Eocene period. Thus the anticlinal line of the Vale of 

 . Wardour, after a course of about six miles east of the Avon, sinks 

 under a saddle of the tertiary beds at, or close upon, the Test. 

 A cursory examination of the country from Michelmarsh and 

 Timsbuiy on the last-mentioned river, by Anfield toward Otter- 

 bourne on the Itchin, gave me some idea of a continuation of 

 this saddle of tertiary sands and clays, with an escarpment in 

 the high grounds of Toothill and Chilworth on the south. But 

 of this I cannot speak with confidence. I am, however, quite 

 assured, that although it may be possible to discover marks of a 

 continuation of this line of elevation eastward, it is not connected 

 with that which I am about to describe, and which issues west- 

 .ward from the south-west corner of the Weald denudation. 

 These two, like the Pewsey and Peasemarsh lines, pass by and 

 do not inosculate with each other. 



[To be continued.] 



VIII. Historical Sketch of the progress of improvement in the ap- 

 plication of Electro -Magnetism to Geodetical and Astronomical 

 purposes f. By G. P. Bond J. 



THROUGH the kindness of Dr. Bache and Prof. Walker of 

 the United States Coast Survey, I am enabled to give from 



* If Dean Hill had the chalk colour, which it ought to have had, iu 

 Mr. Greenough's map, as ought also the line of high ground running west 

 in the course of the words " proposed canal," then the tertiary colour would 

 have been seen projected north of it, over the localities above specified, 

 toward Salisbury ; the synchnal line being a trough of tertiary beds, and 

 the cause of this projection. 



t Communicated by the Author. 



X The article consists, mainly, of extracts from an official communicatipn 

 from Prof. Walker to the Superintendent of the United States Coast Survey, 

 dated April 24th, 1861. 



E2 



