Yesterday I made a most interesting excursion over all the scene of last year’s battles,--the plain of St Denis, Vertus, the heights of Belleville, Montmartre, &c. Independent of historical associations, these heights are extremely interesting, from the fine commanding views they afford; but particularly in a geological point of view. Rising abruptly to the height of some hundred feet from the (almost level) Plain de St Denis, their appearance is very remarkable as we approach by the great northern road to La Chapelle, almost everywhere terminating in lofty white precipices of gypsum (or sulphate of lime)--hence called plaster of Paris. Montmartre appears once to have been a continuation of the heights of Belleville, from the similarity of the gypsum cliffs opposite to each other. It is now isolated, and, with its precipitous terminations and crest covered with windmills, forms a very remarkable object from the plain below. These windmills are principally on the end over Clichy; towards the other is the celebrated telegraph--known by fame to all Europe--whence were transmitted at various periods orders for the invasion of Italy, Austria, Russia, Prussia, and Belgium, and by which Paris was so often roused to the boiling-point of vanity when it brought intelligence of Jena, Wagram, &c. But _revenons à nos moutons_. The heights are separated by a narrow gorge, in which, under the cliffs of Montmartre, is a small hillock[22] (Mamelon), crowned by three windmills, which appears to have been formed by detritus from above. The dome of St Genevieve seen through this gorge gave us the first notice of the French capital the evening we arrived at Garges.