Obituary — W. A. Parker. 95 



by contiguous portions of the two rectangles. The excess, if any, 

 of lime over available alumina has the silica necessary to form 

 wollastonite, and the excess, if any, of iron oxide over available soda 

 and the magnesia have the silica required to form orthosilicates. 

 The remaining silica space is then divided up to show the additional 

 silica required or available for the felspars, felspathoids, and segirine, 

 and that available to convert the orthosilicates of iron and magnesium 

 into metasilicates. The remainder represents free silica or quartz. 



Dr. G. F. Herbert Smith : " On the use of the Gnomonic Projection 

 in the calculation of Crystals." If projected on to a plane at right 

 angles to the edge of the zone containing the poles from whicli 

 biangular measurements were made, the diagram takes the form of 

 a net, the nodes of which represent the principal poles. ■ The unit 

 lengths of the net are easily calculated from the data, and once the 

 rectangular co-ordinates of any node with respect to axes on the 

 diagram have been determined those of the remainder follow by 

 simple addition or subtraction; the corresponding spherical angles 

 are deduced by a simple calculation. The accuracy of the calcula- 

 tions may be checked from the diagram at every step. To keep the 

 projection corresponding to any crystal within reasonable dimensions 

 it is sometimes convenient to project on to the faces of a cube. The 

 direction of a zone when crossing from one face to another is very 

 simply found from the diagram. 



OBIT"Cr.A^I^~2^. 



WILLIAM ALBERT PARKER, F.G.S. 

 BoKN 1855. Died January 14, 1918. 



We deeply regret to record the death of Mr. W. A. Parker, of 

 Rochdale, which took place on January 14 at the age of 63. For 

 many years he was a highly esteemed schoolmaster in Pochdale. 

 Here lie indulged his taste for scientific research, especially geology, 

 and became associated in friendship with a small but enthusiastic 

 body of geologists, including, amongst others, Walter Baldwin, the 

 late W. H. Sutclifle, Dr. March, James Horsfall, Kobert Law, and 

 S. S. Piatt. Assisted by other members of this band Mr. Parker 

 specially devoted himself to the task of working out the beds of 

 shale, with ironstone nodules containing fossils, of Middle Coal- 

 measure age at Sparth, Rochdale. This led to the discovery of 

 a numerous and rich series of fossils, including rare Orthopterous 

 insects, Arachnida, and Crustacea, many of which have been figured 

 and described in the Geological Magazine (see volumes for 1907, 

 pp. 400-7, 539-49 ; 191 1, pp. 361-6 ; 1913, pp. 352, 356). Anew 

 Crustacean, RocMaleia Parheri, was named after our friend. Many 

 of these valuable specimens are now preserved in the Manchester 

 Museum and in the British Museum (Natural History). His loss will 

 be keenly felt by a large circle of geological friends in the Midlands. 



H. W. 



