522 0^'■ THE SO-CALLED DIOEITE OF LITTLE EISTOTT. 



DlSCFSSIOS". 



Dr. Eya:s's remarked on the interest attaching to the determi- 

 nation of the locality and of the distribution of the specimens. 



Dr. A, Geikie pointed out the remarkable changes in texture and 

 composition in the rocks of this class within short distances. This 

 is illustrated by the Inchcolm and Bathgate rocks and by certain 

 intrusive rocks in the north of Ireland. 



Mr. Teall pointed out that the term picrite, first used by 

 Tschermak, had been applied by later writers to rocks differing 

 somewhat from the original type ; and also that Cohen, who applied 

 the term to the Schriesheim rock, under the mistaken idea that the 

 dominant bisilicate was diallage, now wished to withdraw this name 

 from the rock altogether. 



Prof. Seelet stated that the specimens of the Henslow collection 

 are all recorded, with full particulars concerning them, in catalogues 

 which are preserved in the Woodwardian Museum. 



Mr. Etjtley thought that possibly picrite was an altered condition 

 of basalt. He regarded the statements made by the late Mr. Clifton 

 Ward as very justifiable. 



Mr. HimLESTox was glad to learn that the rock which yielded the 

 boulders of hornblende-picrite, first noticed by the President, had 

 at length been discovered in Anglesey, so that jS'orth Wales was 

 independent of the Lake District for its supply. He asked for further 

 information concerning the mode of its occurrence in situ. 



Prof. Junn defended the use of the term picrite, and thought that 

 the Author, in giving the name of hornblende-picrite to the rock he 

 had been the first to define, was exercising a wise discretion. 



Mr. BATJEEiiAX thought that picrite, or names very similar to it, 

 had been formerly applied to minerals. He did not think it wise to 

 give similar names to minerals and rocks. 



Mr. Haekee said that the two localities where the rock occurred in 

 Anglese}' are both large dykes intrusive in Arenig rocks. In the Lleyn 

 peninsula are large intrusive bosses. In aU cases the rocks vary in 

 texture and composition within very short distances. The Henslow 

 catalogue does not state whether the rocks were collected «i situ or 

 from boulders. 



Dr. Hicks thought the boulder at St, Davids must have been 

 transported from a distance, though it is possible that the rock 

 would be found in situ in ISTorth- east Pembrokeshire. 



Prof. BoisTraT said the name " picrite" was a weU-recognized name 

 for a rock, and he had employed it as such. It was absurd to sug- 

 gest that such a rock might be derived by decomposition from basalt, 

 as it differed much both chemically and mineralogically. The rock 

 was not, in any proper sense of the term, a decomposition-product at 

 all, but rather a recomposition of another rock. jSTothing he had said 

 in his paper could possibly be represented as reflecting on the late 

 Mr. Clifton Ward, who had recognized the abnormal nature of the 

 rock, and had done such excellent work in his day. 



