710 ME. R. H. E.ASTALL OX TEE GEOLOGY OF [NOV. I9II, 



The marble is a white or greenish-white rock of fine texture, 

 and very uniform in character. In a slice [9460] it is seen to 

 consist entirely of carbonates, with no other recognizable minerals. 

 A sample was subjected to qualitative chemical tests, and showed 

 no trace of either magnesia or iron, and no matter insoluble in 

 hydrochloric acid ; it must, therefore, consist wholly of calcium 

 carbonate, and is consequently a rock of remarkable purity. 



A specimen of the black limestone from the other side of the 

 quarry was also examined in the same way : it was found to be 

 wholly soluble in hydrochloric acid. When the solution was 

 neutralized with ammonia, a very small precipitate came down, 

 which probably contains both iron and alumina. A trace only of 

 magnesia was also found. The iron, alumina, and magnesia were 

 all too small in amount for quantitative determination, and the 

 rock is practically pure calcium carbonate : therefore the chemical 

 composition is not inconsistent with the view that this limestone- 

 band is the same bed as the white marble, but less metamorphosed. 



(2) The Granitic Intrusions. 



About a mile north of Worcester are to be seen over a con- 

 siderable area frequent outcrops of a rock which has been com- 

 monly referred to as ' phyllite-gneiss.' This is a massive strongly- 

 foliated rock of a grey colour, nearly always distinctly lenticular, 

 and often showing sericitic mica on broken surfaces. It is quite 

 apparent, both from a petrographical examination and from field- 

 relations, that this ' phyllite-gneiss' represents masses of granite or 

 granite- porphyry which have been intruded into the sediments at 

 some period prior to the final foliation. The intrusive character 

 is not easy to determine with certainty, but I was lucky enough 

 to find on the ground conclusive evidence on this point. Imme- 

 diately west of the small hill at the foot of which the marble- 

 quarry is situated are several deep sluits, which have removed 

 the sand and loam down to the surface of the solid rock. In one 

 of these sluits, which is about 6 feet wide and 4 feet deep, there 

 can be seen a contact of the phyllite-gneiss and the slate. Prom 

 this it is clear that the granite was intruded after the major 

 joints of the sedimentary deposit had come into existence, since 

 the transgression is controlled by these ; but both sediment and 

 intrusion alike were affected by the latest and most powerful 

 pressure, which produced parallel foliation in both. 



When examined with the microscope [9461-62], specimens of 

 this rock show much less alteration than might be expected from 

 its macroscopic appearance. It is distinctly porphyritic, with 

 phenocrysts of quartz, orthoclase, and oligoclase in a fairly fine- 

 textured ground-mass of granulitic type, consisting of quartz and 

 felspar. Some patches of a dark-green chloritic mineral probably 

 represent original biotite. This rock is a granite-porphyry or 

 quartz-porphyry, of fairly acid composition and alkaline affinities. 



A series of specimens of this rock collected from different points 



