BV W. N. BENSON. 159 



secondary origin of the albite, unless, in some circumstances^ 

 albitising solutions have no action on pyroxene. Certainly some 

 decomposition-products occur, chlorite, epidote, and calcite, but 

 they are not abundant^ save in rocks that have obviously been 

 in solution-channels (i.e., shear-lines, and the boundaries of some 

 sills) or have suffered the intense pressure that affected the rocks 

 of the Woolomin Series. It must be noted, however, that our 

 rocks are rarely, if ever, flows, and, as Messrs. Flett and Dewey 

 have observed, pyroxenes, as a rule, are better preserved in the 

 intrusive than in the extrusive rocks. Further, in the examina- 

 tion of the wide sills, there is no sign of greater albitisation of 

 the upper parts. One cannot say definitely which is the upper 

 part of the great sills on Munro's Creek and Hanging Rock, but 

 it seems clear that the rock is equally albitised throughout a 

 width of more than five hundred yards. The western, and pro- 

 baV)ly upper side of the former mass contains veins of albite- 

 dolerite-pegmatite. Another point of difference from the British 

 spilitic rocks is the albitic character of the felspar in the quartz- 

 dolerites. Certainly, in some quartz-dolerites, zoned felspar 

 occurs, of which the central portion is andesine, but it is not 

 usually present. They are, however, with the single exception 

 noted, the only rocks in which felspar more basic than oligoclase 

 is to be found. 



Again, adinole is not developed along the contact of dolerites 

 and cherts. Two specimens were analysed, which should have 

 had every opportunity of becoming albitised had sodic solutions 

 escaped from the cooling magma. These are (A) the chert in 

 the mass betAveen the pillows of spilite, illustrated in Fig. 2b, and 

 (B)the secondary chert from the specimen shown in Fig. 1, in 

 which the felspars of the invading dolerite(1040) are clear well 

 crystallised prisms of labradorite. C and D are respectively 

 radiolarian chert and cherty shales from the Tamworth Common. 

 (A narrow sill of albite-dolerite occurs here, but, from the de- 

 scriptions of Messrs. JJavid and Pittman(12), it does not appear 

 to have been in contact with these two rocks). The figures are 

 those determined by Mr. Mingaye. E and F are from slightly 

 altered, aud completely altered sediments, that are changed into 



