The Rev. S. Haughton on Serpentines and Soapstones. 253 



The degi-ee of success which I have obtained without the op- 

 portunity of satisfying these requirements, is sufficient to assure 

 me that these beautiful experiments may thus be placed within 

 the reach of all, and to justify the expectation that any one who 

 possesses the necessary skill and other advantages may convert 

 this, not only into a popular, but an accurate and scientific ex- 

 periment. 



Besides the lines giving lateral spectra, I have produced regular 

 series of a large number of circles, triangles, &c. within the space 

 of the pupri of the eye, so that the phsenomena may be seen in 

 a variety of forms by the unaided eye*. This is, 1 suppose, 

 scarcely possible by any other means than photography. 



XXXII. Notes on Mineralogy.— ^o. III. On Seipentines and 

 Soapstones. By the Rev. Samuel Haughton, Professor of 

 Geology in the University of Dublin-^. 



n^HE following additional analyses of serpentines and soap- 

 J- stones may be considered of interest by some of your 

 readers, particularly those relating to the serpentine porphyry 

 of the Lizard, respecting which there has been some difi"erence of 

 opinion among mineralogists. 



The serpentine porphyry of Cornwall consists of greenish 

 crystals imbedded in a reddish paste; the green mineral has 

 been pronounced diallage by Dr. Boase and Sir H. De la Beche, 

 and the reddish paste considered by the same authorities as a 

 species of felspar : both these opinions seem to me to be erro- 

 neous, as the porphyritic serpentine of Landewednack and Ky- 

 nance Cove must be considered as composed altogether of ser- 

 pentine. I have not found alumina in sensible quantity in the 

 Cornish porphyry, and therefore its presence in the veins of 

 steatite which intersect the serpentine porphyry is highly inter- 

 esting. During a visit which I paid to this interesting locality 

 in 1854, I ascertained the cause of the presence of alumina in 

 the veins of soapstone. Both at Kynance Cove and Gue Grease, 

 the serpentine porphyry is intersected by dykes of granite, and 

 the celebrated veins of soapstone lie spread out in sheets at the 

 junction of the serpentine and granite; the soapstone must 

 therefore be regarded as the result of the contact of these rocks 

 at an elevated temperature ; the serpentine supplying the mag- 

 nesia; and the felspar of the granite, the alumina, necessary for 

 the formation of the soapstone. 



* But miicli better with a conuuon telescope, 

 t (^oniinunirated bv the Author. 



