42 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. 



a rough experiment made in the field to test the comparative 

 specific gravity of solid and molten lava. Another related to the 

 occurrence of diamonds in S. Africa in volcanic rock at a greater 

 depth than the superficial shales through which it had burst, a fact 

 at variance with the hypothesis advanced by a previous author that 

 the diamonds were derivates of the hydrocarbons contained in the 

 shales. 



Micro-petrology. — Five petrological papers dealt with the intimate 

 structure of rocks, a number which appears small considering the 

 activity with which the microscopic investigation of rocks has been 

 pursued during the three decades which have elapsed siuce the great 

 impulse given to this branch of research by Dr. H. C. Sorby's paper 

 " On some Peculiarities in the Microscopic Structure of Crystals applic- 

 able to the determination of the Aqueous or Igneous Origin of Minerals 

 and Hocks," published in the Society's Journal in 1851. Since that 

 epoch petro-microscopy has attained an importance that can hardly 

 be overestimated. Each successive vear has yielded fresh evidence 

 of its value, which has, perhaps, seldom been more aptly illustrated 

 than in Prof. Bonney's paper " On the Hornblendic and other 

 Schists of the Lizard District," a locality which the labours of one 

 of our founders, who was also one of the fathers of the Geological 

 Survey of the United Kingdom, Sir Henry De la Beche, have 

 rendered classic ground. 



Amongst the stratigraphical papers, probaWy second to none in 

 interest were : — " A Comparison of the Cambrian Strata of the 

 Russian Baltic Provinces with those of Scandinavia and Great 

 Britain," by Dr. F. Schmidt, in which he argued for the unbroken 

 continuity, in those provinces, of the Cambrian, Ordovician, and 

 Silurian Systems ; Prof. Lapworth's comprehensive and elaborate 

 memoir " On the Girvan Succession," in which he offered a de- 

 monstration of the true successional order of the Girvan series of 

 Palaeozoic rocks, based principally on their fossil contents. Should 

 this new reading of the. Girvan beds stand the tests of time and. 

 adverse criticism, its author may well find satisfaction in having 

 achieved a success which many other able workers in the same field 

 failed to secure ; and, lastly, Dr. Hicks's paper " On the Metamorphic 

 and Overlying Bocks in parts of Boss and Inverness Shires (with 

 petrological notes by Prof. Bonney)," in which the author offers a 

 demonstration, based on stratigraphical and petrological evidence, 

 that the large group of rocks in those districts, hitherto regarded as 

 metamorphosed Silurian, are really members of the much earlier 

 Archaean system. The question is one of much importance ; and, 

 however it may be finally settled, it is a matter of congratulation 

 that it has engaged the attention of so earnest a worker, and one 

 whose labours amongst the earliest crystalline rocks in other districts, 

 have been deemed to merit the Bigsby Medal. 



An analysis of all the subjects treated of during the Session has 

 brought out what perhaps might not be generally anticipated, a 

 great preponderance of p.zlceontological papers. Their number 

 actually exceeds that of those on stratigraphy and topography and 



