RECENT ADVANCES IN SCIENCE 397 



Arenig Sea, until the Baltic region became dry land, and Scan- 

 dinavia was joined to Armorica. These movements appear to 

 have been simultaneous in Europe and North America. 



The work of Raymond and Twenhofel has been directed 

 to many of the same problems as that of Grabau and Reed. 

 Twenhofel states that coral reefs exercised a controlling influence 

 in the development of the lithology and stratigraphy of the 

 famous Silurian area of Gotland. 



The unravelling of the Palaeozoic and Pre-Cambrian strati- 

 graphy of the Rocky Mountains and Great Basin regions is 

 being prosecuted with vigour, as shown by the important papers 

 of Tomlinson, Ransome, Noble and Hunter. 



Bailey's paper on the Islay Anticline deals again with the 

 vexed questions of the succession and structure of the Highland 

 Schists. The complexity of the district forbids any short 

 statement of his results, but Mr. Bailey's interpretation is at 

 variance with that advanced by the Geological Survey in 

 the official memoir upon the district, especially as regards the 

 structure of the northern part of the island. 



In Rajputana Mr. Heron distinguishes an Archaean series 

 of schists, crystalline limestone, and quartzite, intruded by 

 granites (Aravalli system), which is separated by violent un- 

 conformity from the overlying Delhi system of thick limestones 

 and quartzites. The great break is probably near the horizon 

 of the Eparchaean unconformity of the North American geolo- 

 gists. 



Petrology — Igneous Rocks 



Daly, R. A., The Geology of Pigeon Point, Minnesota, Amer. Journ. Sci. (4), 



1917,43, 423-48. 

 Bowen, N. L., The Problem of the Anorthosites,/<?«r«. Geo/. 1917, 25, 209-43. 

 Tyrrell, G. W., The Picrite-Teschenite Sill of Lugar, Ayrshire, Q.J.G.S. 1917, 



72, pt. 2, 84-131. 



Some Tertiary Dykes of the Clyde Area, Geol. Mag. (6), 1917, 4, 305-1 5, 350-6. 



Holmes, A., Albite-Granophyre of Carrock Fell, ibid. 403-7. 



Smith, H.G., The Lurgecombe Mill Lamprophyre, Q.J.G.S. 1917,72, pt. 2,77-83. 



Lacroix, A., Les Laves a hauyne dAuvergne et leurs enclaves homceogenes : 



importance theorique de ces derniers, Comptes Re?idus, 191 7, 163, 581-8. 

 Bowen, N. L., The Sodium- Potassium Nephelites, Amer. Journ. Sci. 1917,43, 



115-32. 



Pigeon Point on Lake Superior is one of the classic cases of 

 the development of " red rock " (micropegmatite) in a gabbroid 

 magma. Originally described by Bayley as a great dyke, it is 



