are extremely variable in quality, structure, and composition, being sometimes so soft as to produce kaolin, or porcelain clay ; sometimes hard and dura ble ; again, they are frequently schorlaceous and porphyritic, as at Land’s End. 1 In composition, there are also varieties containing two felspars, pink and white; or two micas, grey and black. 2 The principal quarries are those near Liskeard (already referred to), those of Lamorna, west of Penzance ; Penryn, near Falmouth; and Mill Hill, in Maldron. The stone from those quarries is of excellent quality. The granites of Devon and Cornwall have been shown by Sir H. De la Beclie to be of an age inter mediate between the Lower Carboniferous and Tri- assic periods. 3 The following are some of the principal works which have been constructed in part, or altogether, of Cornish granite : The Portland breakwater, from Pen ryn and Lamorna quarries ; the Keynliam Docks ; the Commercial Docks, London ; the Birkenhead Docks ; the National Works at Chatham and Portsmouth, from the same localities; the Wellington monument at Strathfieldsaye, the shaft of the column being of one solid block thirty feet in height, from Constantine. 1 See a good representation of this porphyritic granite in Lyell’s Student’s Manual of Geology, p. 540. 2 A fine collection of varieties of granite from the neighbourhood of Penzance is to be seen in the Mus. of Trinity College, Dublin. 3 Geological Observer, p. 563.