Composite Spherulites in Obsidian from Hot Springs. 123 



2. Rhyolites ; 3. Gneissic rocks ; 4. Slates like those of the under- 

 lying group. The supposed Archaean masses on the western 

 border are non-existent, being intrusive and transgressive igneous 

 rocks. 



The volcanic group on the east is not bounded by the main fault, 

 the dark shales lying to the east of that fault. Evidence is given 

 that the volcanic rocks have been protruded through these shales, 

 which they have altered. The Eurite of the Wrekin is of later date, 

 and the only possible older rocks are the Rushton Schists and the 

 fragments of schistose rocks on Primrose Hill. 



At several places patches of red grit and conglomerate are seen on 

 the Volcanic hills ; these are referred to the Cambrian, and their 

 connexion also with earlier conglomerates forming part of the Vol- 

 canic series is suggested. The Cambrian quartzite is later than all 

 these, but may be synchronous with the upper part of the western 

 Grits. 



The Volcanic rocks are not, therefore, Middle Monian, as formerly 

 supposed, but represent the interval between Monian and Cambrian. 

 If classed with either, the author inclines rather to place them with 

 the Cambrian, in spite of the unconformity of the quartzite. He 

 regards them as probably the equivalents of the Bangor Series, and 

 possibly of the St. David's Volcanic Group. If this classification be 

 adopted, then the Monian system will be entirely separated from the 

 Pebidian, and be established od distinct and independent obser- 

 vations. 



3. " On a Crocodilian Jaw from the Oxford Clay of Peterborough." 

 By R. Lydekker, Esq., B.A., P.G.S., &c. 



4. "On two new Species of Labyrinthodonts." By II. Lydekker, 

 Esq., B.A., E.G.S., &c. 



March 26.— J. W. Hulke, Esq., E.R.S., Vice-President, 

 in the Chair. 



The following communications were read : — 



1. " On a new Species of Gyphaspis from the Carboniferous rocks 

 of Yorkshire." By Miss Coignou, Cambridge. 



2. " On Composite Spherulites in Obsidian from Hot Springs, near 

 Little Lake, California." By Erank Rutley, Esq., E.G.S., Lecturer 

 on Mineralogy in the Royal School of Mines. 



The spherulites which form the subject of the present communi- 

 cation have been previously noticed, and it was then suggested that 

 a smaller spherulitic structure was set up in the large spherules after 

 their formation. In the present paper evidence was adduced in favour 

 of a different mode of origin. It was argued that the small spherulitic 

 bodies (primitive spherulites) were developed in the obsidian before it 

 assumed a condition of rigidity, and that they floated towards certain 

 points in the still viscid lava, and segregated in more or less spherical 

 groups, though there is no evidence to show what determined their 

 movements ; furthermore, that from a point or points situated at 



