390 J. CLIFTON WARD ON THE MICROSCOPIC STRUCTURE OF 



Tyrol ; quartz trachyte, and another volcanic rock from Peru ; and 

 some few metamorphic and sedimentary rocks. 



The first of a series of valuable papers by Mr. Allport appeared in 

 1869 *; in it the author described the basalt of S. Staffordshire, and 

 noted the presence of pseudomorphs after olivine. In the following 

 year the same author contributed a paper on the " Basaltic Rocks of 

 the Midland Coal-fields " f, showing that the traps of " Kinlet and 

 Shatterford (west of Kidderminster), the Clee Hills, Little Wenlock 

 (near the Wrekin, in Shropshire), Coalville (near Bardon Hill, in 

 Leicestershire), and Matlock (in Derbyshire)," were all basaltic. In 

 another paper, in the same year, upon the " Microscopical Examina- 

 tion of Rocks and Minerals "J, Mr. Allport showed that the traps 

 of the AYarwickshire Coal-field contain hornblende instead of augite, 

 and are therefore true diorites ; at the end of the paper the author 

 states his belief " that the following results of microscopical exami- 

 nation will stand the test of further study : — 



" 1. The mineral constituents of the melaphyres and other fine- 

 grained igneous rocks may be determined with certainty, a result 

 which has not been attained by any other method of examination. 



" 2. The mineral constituents of the true volcanic rocks, and those 

 of the old melaphyres, are generally the same. 



" 3. The old rocks have almost invariably undergone a considerable 

 amount of alteration; and this change alone constitutes the difference 

 now existing between them and the more recent volcanic basalts." 



In 1871 Mr. Allport again contributed two papers, one " On the 

 Microscopic structure and Composition of a Phonolite from the 'Wolf 

 Rock'"§, and the other on the " Relative Ages of Igneous Rocks" j|. 

 In the former, the structure of the rock is shown to be similar to 

 the Tertiary Phonolites, and an analysis is given. In the latter the 

 author concludes " that there is no essential difference between 

 eruptive rocks of different geological epochs," and states, " I arrived 

 at this conclusion more than three years since." 



In the same year (1871) Prof. Zirkel published a valuable memoir 

 entitled "Geologische Skizzenvon der Westkiiste Schottlands"*j[, in 

 which he gave descriptions of the microscopic structure of many of 

 the volcanic rocks of the western islands. 



In 1872 follow papers by Mr. Allport " On the Microscopic Struc- 

 ture of the Pitchstones and Pelsites of : . Arran"**. At p. 537 the 

 bases of the pitchstones and the felsites'are contrasted — the former 

 being " a homogeneous glass without a trace of double refraction" 

 the latter having a felsitic structure which " invariably exhibits 

 double refraction" and " as either of the prisms is rotated, the mass 

 appears to break up into variously coloured little patches, which 

 gradually assume a more definite form as the axes approach to a 

 right angle." None of the rocks described, however, seem to be con- 



* Geol. Mag. vol. vi. p. 115. t Ibid. vol. vii. pp. 159-102. 



t Ibid. vol. vii. pp. 431-435. § Ibid. vol. viii. pp. 247-250. 



j| Ibid. vol. viii. pp. 448-450. 



% ' Zeitschr. d. deutschen geologischen G-eeellschaft,' Jabrg. 1871, pp. 1-124. 



** Geolog. Mag. vol. ix. pp. 1-9 and 536-545. 



