Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/241



APPENDIX.

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On the Dykes of Monte Somma in Italy,

Extracted from a Series of Letters addressed to the late

LORD CHARLEMONT, P.R.I.A.

By the late Rev. GEORGE GRAYDON, Fellow of Trinity College Dublin.

Dated Naples.

“ appearance of the face of the cliff of Monte Somma in its, whole length perfectly coincides with the idea given by its semicircular shape, surrounding Vesuvius, as well as by its sloping back as seen from Naples, and strongly confirms the opinion of its having once formed a much higher conical hill.”

“ The face of the cliff viewed on a horizontal line is by no means smooth, but considerably indented in some places into semicircular or more than semicircular hollows or recesses, with sides nearly perpendicular; in others into hollows with steep sloping sides down which the sand and stones are continually sliding.”

“ It is formed of a great number of successive strata of lavas, in some places perhaps upwards of thirty; these strata in general are thin, that is, not exceeding from three to six feet in depth of solid stone, the intervals between them, which are generally much thicker than the strata themselves, consist of porous red or calcined and usually


 * This gentleman presented a series of volcanic specimens, collected by himself on Vesuvius, to the Royal Irish Academy; vide Kirwan's Mineralogy, ed. 1794, vol. 1. preface, page xv, where he is much commended.