Humboldt-Universität (Berlin) provides access to some old scanned book, including 4-volume collection of papers by Leopold von Buch These are:
Leopold von Buchs gesammelte Schriften. erster Band, 1870
Leopold von Buchs gesammelte Schriften. zweiter Band, 1870
Leopold von Buchs gesammelte Schriften. dritter Band, 1877
Leopold von Buchs gesammelte Schriften. vierter Band, 1885
hyperlinks lead to pages with direct links to .pdf-files of the whole volumes or to .xml-pages with list of all articles and access to page-by-page view
Here there is list of articles from the 4th volume: http://edoc.hu-berlin.de/ebind/mfn/buch_4_MN0012751/XML/
This volume devoted mainly to stratigraphical & paleontological papers by Buch, which follow from figures with ammonites, bivalves, etc
