152 PROFS. LLOYD MORGAN AND REYNOLDS ON THE [Ma)* I904, 



(1) Description of the Lavas of Goblin Combe. 



The rock seen in situ at the more westerly exposure is a highly 

 amygdaloidal olivine-basalt. In a hand-specimen it shows pseudo- 

 morphs after olivine, and vesicles which may be more than half an 

 inch in diameter, and are sometimes empty, sometimes filled with 

 calcite and a green chloritic mineral. Microscopically, the most 

 prominent mineral is altered plagioclase, in laths having an average 

 length of about 0*4 millimetre and a diameter of 0*04 mm. The 

 spaces between the laths are partly filled up by a brown, nearly- 

 isotropic substance, but chiefly by green patches of serpentinized 

 pyroxene and by calcite. Dark rods, once magnetite, but now replaced 

 by the peroxide, are very plentifully scattered. The phenocrysts, 

 which are large and prominent, are entirely represented by patches of 

 a carbonate, probably calcite, and from the perfect preservation of the 

 form of some of these it is clear that they represent olivine-crystals. 



The olivine-dolerite or basalt which occurs in blocks on the 

 surface of the ground near the more easterly of the Goblin-Combe 

 exposures is the handsomest of all the igneous rocks of the district. 

 It consists of fresh plagioclase-laths with a maximum length of about 

 0*5 millimetre ; fresh brown augite, occurring in grains filling up 

 the interstices between the laths, and also forming phenocrysts and 

 polysynthetic crystals which reach a length of slightly over a milli- 

 metre ; magnetite in long needles ; and olivine, now completely 

 converted into green serpentine, but showing the crystalline form 

 excellently. (See PI. XVII, fig. 1.) 



(2) Description of the Lava of Spring or Birnbeck 

 Cove, Weston-super-Mare. 



The lava here is a rather interesting basalt, and resembles all the 

 other rocks of the section in being stained a deep red. No pheno- 

 crysts are visible in a hand-specimen, but there are, as a rule, 

 numerous amygdules of calcite which reach a maximum diameter 

 of 3 millimetres. Hand-specimens, too, taken from certain parts of 

 the flow, show numerous other circular red bodies which prove, 

 when examined microscopically, to be varioles. The groundmass is 

 abundant, and is seen in section to show numerous felspar-needles ; 

 apart from these, it is practically isotropic, and must have been 

 originally, to a large extent, glassy. It is, however, much obscured 

 by the abundant red oxide of iron. The varioles above referred to 

 reach a large diameter (3 millimetres), and are very sharply defined. 

 They are, however, much altered, and are obscured by the iron-oxide 

 which is sometimes uniformly distributed through them, sometimes 

 forms a peculiar network traversing them, and is occasionally collected 

 along lines which radiate inward from the circumference for a short 

 distance with extreme regularity. (See PI. XVII, fig. 3.) 



The chief phenocrysts present are a few felspars in a greatly- 

 altered state. The large amygdules are rilled with well-cleaved 



