VOL. LXV.] PHILOSOPHICAL TRANSACTIONS. 677 



lip in another separate box, to be sent you for comparisonj but forgotten by my 

 servant. They will be sent hereafter. The sassa, the tree which produces the 

 opocalpasum, does not grow in Arabia. Arabian myrrh is easily known from 

 Abyssinian by the following method : take a handful of the smallest pieces, 

 found at the bottom of the basket where the myrrh was packed, and throw them 

 into a plate, and just cover them with water a little warm ; the myrrh will remain 

 for some time without visible alteration, for it dissolves slowly ; but the gum 

 will swell to 5 times its original size, and appear so many white spots among the 

 myrrh. The pieces sent are, N° 1, Virgin Troglodyte myrrh. N" 2, the 

 worst sort of Troglodyte myrrh, called cancabs. N" 3, Opocalpasum from the 

 myrrh-country. 



XLI. An Account of a curious Giant's Causeway, or Group of Angular Co- 

 lumns, newly discovered in the Euganean Hills, near Padua, in Italy. By 

 John Strange, Esq. F.R.S. Dated Venice, March 10, 1775. p. 418. 



This phenomenon is situated at Castel Nuovo, a small village near Teolo, in 

 the Euganean hills, about 4 miles south-west of the other Giant's Causeway of 

 Monte Rosso before described. II Sasso di San Biasio, which is the name of the 

 spot where this causeway is situated, is a large insulated rock, composed of the 

 same sort of grey granite that is common to the Euganean hills, before described. 

 The columns which form this r:auseway, partly against the flank of the rock, 

 and partly round its base, are of the same substance with the rock itself, to 

 which they adhere, as I have constantly observed in all similar groups. They 

 are therefore of a compound nature, like the columns of Monte Rosso, and 

 differ entirely from the common sort, which are mostly homogeneous, or of a 

 uniform texture ; as is observable in the jointed, as well as simple species of 

 basaltes. By comparing the pieces of these columns with the fragments of the 

 columns of Monte Rosso, before transmitted to the society, some essential dif- 

 ference will appear between them. Those of San Biasio, though very hard, are 

 rather porous, of a lighter colour than the columns of Monte Rosso, and very 

 much resemble a species of lava. 



This porousness Mr. S. once before observed, and more signally too, in some 

 basaltic columns near Achon, in the province of Auvergne, in France. The 

 pores in the columns of both these groups are also irregularly dispersed, and of 

 unequal size, like those of pumice stones and other common pori ignei. Those 

 of the columns of San Biasio are commonly invested with a sort of crocus martis 

 frequently observed in the pores of other vulcanic concretions. These properties 

 are surely further marks in favour of the igneous origin of such columnar crystal- 

 lization ; especially, since they seem contrary to the principle by which the 

 common aqueous crystals are formed, successively, et per juxta-positionem par- 



