735 
describing a rock texture. Lyell uses tbe word in describing that granite in which large 
crystals o£ felspar, usually orthoclaso, are sometimes scattered through an ordinary 
base of granite. 
I have measured crysfaLs in the porphyritic grarite of Dartmoor two inches in 
length, and Lyell mentions crystals measurijig three inches in length in the porphyritic 
granite of the Land’s End.* 
The rocks are so variously named by different writers that it is not easy to be 
precise in definition. Eor instance, Judd, after examining some of my sections, states in 
a letter to me that “ the rocks named ‘ Queensland granite ’t belong to the class of 
quartz-diorites (tonalite.s) which appear to be very abundant in Queensland. They were 
recognised as such by the late Mr. li. Daintree.” 
The diorites are very poorly represented in the Collection. They call for no 
summarising. 
In the rocks grouped under the head of porphyrites it is otherwise. The 
Croydon series is of interest, as are also the two, ?sos. 79 and 80, from the Great 
Northern Tin Mine, Herberfon. The sections from this porphyrite dyke show how 
much more the quartzes have suft’ered from erosion at the 30L)-feet level than is the 
case with the samples from the surface. No. 32, from the Peak, New South Wales, is 
remarkable for the size of the felspars. The artist had to draw this really striking 
section on a very much larger surface in order to illustrate the two sets of felsjiar twins 
(Vide Plate 00). 
1 should have liked to have learned something from the Gympie “ greenstone ” 
sections ; hut neither Mr. Rands nor myself came to any definite conclusions. In Mr. 
Jack’s “ Mineral Wealth of Queensland,” published in 1888, he says : — “ The greenstone 
of Gympie has long formed a subject of controversy .... even in microscopic 
sections, these rocks are much altered and ‘masked’ by viridite.” 
INDEX TO PLATES. 
Plate 60. — Intrusive Dyke-stone from the Peak, New South Wales. C. S. Wilkinson’s 
Collection. With polarizer only, magnified 50 diameters. 
Plate 61, Fig. 1. — Rhyolite . — Nell Island, Now Guinea. Sir W. Maegregor’s Collection. With 
polarizer onfv, magnified 42 diameters. 
„ Fig. 2. — „ Nell Island, New Guinea. Sir W. Macgregoi’’s Collection. With 
parallel niools, magnified 42 diameters. 
Plate 62, Fig. 1. — „ Nell Island, New Guinea. Sir W. Maegregor’s Collection. With 
crossed nicols, magnified 42 diameters. 
„ Fig. 2. — ,, Hamilton, Mackay, Queensland. A. G. Maitland’s Collection. 
With crossed nicols, magnified 27'6 diameters, showing fluxion- 
structure. 
Plate 63, Fig. l.—Tachylite. — Queensland. R L. Jack’s Collection. With polarizer only, 
magriifled 27'5 diameter.s. 
„ Fig. 2. — Ciuartz. with tourmaline crystals , — With polarizer only, magnifled 42 
diameters. Cooktown. A. J. Madden, Esq., collector. 
Plate 64, Fig. 1. — An interesting unnamed rock, from Cape Upstart, collected by E. L. Jack, 
partially prepared by him and finished by the Author. Mr. Jack 
has no more of the rock left, the whole chip having been ground 
away. Between crossed mools, magnified 27’5 diameters. 
* Sir Charles Lyell. Elements of Geology, 2nd Edition, p. 566. 
t The granites referred to are from Cooktown, John Bull, Bavenswood, and at about 700 feet down 
the Queen Block Extended shaft. Charters Towers. 
