F. W. Mueller — Hocks from Arabia Petrcea. 267 



V. — Notes on sobie Books from Arabia Petr^a. 



By F. W. Etjdler, F.G.S., 

 of the Museum of Practical Geology. 



PROFESSOR HULL, soon after his return from Palestine, was 

 good enough to place in my hands, for microscopic examination, 

 a collection of twenty sections of rocks prepared from specimens 

 obtained in the course of his expedition. Subsequently I had the 

 advantage of receiving thirteen small specimens of the rocks from 

 which some of the sections had been cut ; and respecting these rocks 

 some lithological notes have been published as an appendix to Prof. 

 Hull's Memoir. 1 At a later date I received seven other rock- 

 specimens, representing the remaining sections in my charge ; but 

 for want of time these were laid aside unexamined until it was too 

 late to refer to them in the published work. The object of the 

 present notes is therefore to offer brief descriptions of these remain- 

 ing rocks. At the same time I gladly seize this opportunity of 

 correcting some errors which unfortunately crept into the previous 

 descriptions. 



I. Pale Pink Granite, from a Dyke Penetrating Grey Granite, at Jebel 



Watiyeh. 

 A fine-grained granitic rock, consisting mainly of opaque white 

 felspar and hyaline grey quartz, speckled with a few dark green 

 patches of an altered mica. It presents a general pinkish grey 

 colour, due to a small quantity of ferric oxide disseminated through 

 the rock, and specially marked on the weathered joint-surfaces of 

 the specimen. The felspar is for the most part very turbid, even in 

 thin sections. Many of the crystals exhibit a zonal structure, which 

 is well defined by the arrangement of the included granular matter. 

 Some of the felspar appears to be orthoclase, in an altered condition, 

 and probably microcline is also present; but most of the felspar is 

 a plagioclase, with extinction angles, in relation to the line of twin- 

 composition, varying from 3° to 14°. In a good deal of the felspar, 

 however, the edges of the hemitropic lainellee are too blurred to 

 allow the exact angles to be taken. Some of the felspar crystals 

 measure in section as much as 3 mm. x 1'5 mm. The quartz is 

 xenomorphous, occurring in the form of clear subangular grains, 

 ranging from 05 to 1 mm. in diameter, and traversed by reticulating 

 lines of pores. Much of it shows a polysynthetic structure in 

 polarized light. A few folia of muscovite, or other white mica 

 with straight extinctions, are distributed through the rock. This 

 mineral may be a secondary product. But the dominant micaceous 

 mineral is a biotite, or dark dichroic mica, occurring in aggregated 

 laminae, and mostly altered, after the habit of the ferro-magnesian 

 micas, to a chloritic mineral. A few acicular crystals of apatite are 

 j>resent, penetrating alike the felspar and the quartz. Some grains 

 of epidote may be detected ; and magnetite is present in small quantity, 

 while scattered through the rock are small patches of hematite and 

 limonite, with here and there a few folia of chlorite. 



1 ' ' Memoir on the Physical Geology and Geography of Arabia Petraa, Palestine, 

 and adjoining Districts," Palestine Exploration Committee (1886). 



