Dyke on Clifton Down. 235 



an allnvlal soil, from what Humboldt says, at page 101, of the aspect of 



the situation of Victoria, the approach to which was marked by the ground 

 becoming smoother, and looking like the bottom of a lake, the waters of 



which had been drained oflF, while the neighbouring hills, only one hundred 

 and forty toises in height, were composed of calcareous tufa ; their abrupt 

 declivities projecting like promontories into the plain, and seeming by their 

 form to indicate the ancient shore of the lake. The elevation of the culti- 

 vated ground is fixed by Humboldt at from 270 to 300 toises (about 

 J72G.51, to 1918.35 English feet) above the level of the sea, an elevation 

 from 81.65 to 273.49 English feet below that of Fair Hill, in the mountains 

 of St. Andrews, Jamaica, where a single grain yielded from twenty-eight 

 ears a return of fifteen hundred for one. 



The seed was obtained by me direct from Caraccas, where Sir Robert 

 Kerr Porter procured it from the place of its growth, and was transmitted 

 by me a second time across the Atlantic, to Dr. Bancroft j hence no doubt 

 can be entertained of its being the genuine wheat spoken of by the illus- 

 trious traveller from Prussia. This wheat having been acclimated by such 

 a lengthened period of cultivation within the tropics, was undoubtedly the 

 most proper for the commencement of these experiments ; but it will 

 neverthless be desirable to follow them up by trials with other varieties of 

 wheat cultivated in Europe, some of which, without being inferior in pre- 

 cocity to that of Victoria, may prove perhaps, if possible, more prolific. 

 The advantage of a top dressing has been seen, in the experiment tried by 

 Mr. King on his estate at Charlottenberg, four thousand feet above the 

 level of the sea, (where the Trifolium incarnatuni has also flourished 

 vigorously, and ripened its seed,) and hence the importance of attending 

 to this, and varying the experiments with lime and other sorts of manure, 

 is evident. Altogether, the subject is one which merits the consideration, 

 not only of the Colonial Legislatures, but of the British Parliament. 



Plymouth, August 24, 1835. 



(To the Editor of the West of England Journal.) 



My dear Sir, 



While pointing out to a friend a few of the principal geological 

 features of this district, I was induced to examine that portion of Clifton 

 Down, near to the observatory, which in the various geological sections of 

 that part, particularly those in the first volume of the Geological Trans- 

 actions, second series, is coloured as a dyke in the carboniferous limestone, 

 filled with magnesian or dolomitic conglomerate, represented by a wall of 

 about one hundred feet long, fifteen feet high, and from three to seven 

 feet thick, standing out abruptly in a southerly direction from the great 

 mass of St. Vincent's rocks. 



The error in considering this as a dyke of conglomerate, must have 



