RevifAVs — The Porto Rico Earthquake of 1918. 377 



The Porto Eico Earthquake of 1918. Report of the Earthquake 

 Investigation Commission. By H. F. Reid and S. Taber. 

 Washington. 1919. 



rPHE authors of this valuable memoir are experienced seismo- 

 -^ logists. Professor Reid wrote the second volume of the great 

 report on the Californian earthquake of 1906, Mr. Taber has published 

 accounts of several minor shocks in the United States. The earth- 

 quake here studied occurred without warning on October 11, 1918, 

 shortly after 2 p.m. (Greenwich mean time), lasted two minutes, and 

 was one of the most severe shocks felt on the island since its occupa- 

 tion by Europeans. Considerable damage to jDroperty occurred in 

 the north-western corner of the island, and, from the distribution of 

 the damage and from the evidence of the seismic sea-waves, the 

 authors place the epicentre in the north-eastern part of Mona 

 Passage (between Porto Rico and San Domingo). They consider 

 that the earthquakes were caused by sudden fractures of the rocks 

 forming the ocean-bed, and that the fractures probably occurred 

 along an old fault. It is clear that the crust is still subsiding in the 

 district surrounding the epicentre, for during the last half-century 

 there has been a slow depression of the neighbouring coasts of 

 Porto Rico. Soundings near this coast have revealed the existence 

 of an extraordinary submarine valley running in a north-westerly 

 direction and bounded by slopes which are so precipitous (amounting 

 to 31- kilometres in less than 15 kilometres) that they can only be 

 explained as the result of faulting. A sudden fracture and vertical 

 displacement of the rock along a fault or faults near the head or on 

 one side of this depression would, as the authors remark, account for 

 all the phenomena of the earthquake. The memoir, which is one of 

 the most important of recent contributions to seismology, concludes 

 with a description of the Virgin Islands' earthquakes of 1867-8, 

 and a catalogue of all known earthquakes felt in Porto Rico and the 

 Virgin Islands from 1772 to 1918. C. D. 



On Pitchblende, Monazite, and other minerals from Pichhli, 

 GrAYA District, Bihar and Orissa. By G. H. Tipper. 

 Rec. Geol. Surv. India, vol. i, 1919, pp. 255-62, with three 

 plates. 



\ DESCRIPTION is given of an interesting occurrence of rare 

 -^ minerals in a large mass of pegmatite intrusive into 

 garnetiferous mica-schists. The pegmatite consists of quartz, 

 microcline, and greenish mica with pink garnets and apatite. The 

 pitchblende remains as cores in rounded nodules of uranium ochre 

 formed by its oxidation. A few examples were found of cubo- 

 octahedral pseudomorphs of uranium ochre after uraninite. 

 Torbernite and less commonly autunite are found encrusting mica, 

 apatite, and other minerals. Monazite forms isolated crystals and 



