﻿360 MR. FREDERIC P. MENNELL ON THE [Aug. I9IO,. 



Commissioner's house, and I have also several specimens from 

 Gatling Hill, not far away. Though always uralitized, etc., the 

 structures of these rocks are marvellously well preserved, and there 

 is no difficulty in recognizing their original character. The fol- 

 lowing may be noted as represented among my slides : — Perlitic 

 and spherulitic rhyolite, porphyritic rhyolite, rhyolite-tuff (two 

 varieties), porphyritic trachyte (two varieties), trachytic tuff, por- 

 phyritic andesite, altered enstatite-basalt, epidotic tuff. The most 

 interesting is, perhaps, the first-named, from Gatling Hill, which 

 has large spherulites, about a quarter of an inch in diameter, while 

 the intervening originally glassy areas show well-developed systems 

 of perlitic cracks. 



It may be noted that, about 12 miles south of Bulawayo, the 

 upper beds of the Conglomerate Series contain fragments of these 

 rocks, thus emphasizing the contemporaneous nature of the latter as 

 regards the lower beds. It should be stated that the well-rounded 

 and miscellaneous character of the fragments, which also include 

 granite, etc., besides the lavas, prevents these beds from being re- 

 garded as tuffs. The true tuffs of the series do not present a 

 markedly fragmental appearance, either in hand-specimens or in 

 the field. 



(4) The Crystalline Limestones. 



North of the Conglomerate Series, and overlying it, at Loma- 

 gundi, occurs a thick series of limestones which range east and 

 west for at least 30 or 40 miles. They are well developed near 

 Sinoia, where there is a magnificent series of caves, leading into 

 a huge swallow-hole with an underground pool of deep-blue water, 

 which presents a most extraordinary spectacle. As a term for 

 convenient reference, the name of this locality may therefore be 

 applied to these beds. I have traced this belt through the Alaska 

 Copper-Mine, past Magonde's Kraal, about 30 miles west of 

 Eldorado Mine. The rock, which is usually massive, white, and 

 finely crystalline, is some thousands of feet thick. Near the caves 

 there is a gritty bed close to the top of the limestone, which 

 is succeeded by perhaps 100 feet of reddish slate, and then by 

 quartzite. The limestone is somewhat dolomitic ; and extensive, 

 but little developed, deposits of copper and silver-lea.d ores occur 

 in association with it. 



Other occurrences of limestones, which may or may not be 

 paralleled with the Sinoia rock, are found in various parts of the 

 country, and are probably much more important than at present 

 appears, owing to their more rapid weathering as compared with 

 the associated rocks. Thus a thin band of limestone seems to be 

 interbedded with the Conglomerates on the ' Bowdy Boys' claims, 

 close to the Hunyani Biver. I have also found a large limestone 

 pebble at the fourth level of the Eldorado Mine, whence it would 

 appear that there have been limestones older, as well as younger, 

 than the Conglomerates. A rather dark, coarsely crystalline lime- 

 stone occurs at Chishawasha, near Salisbury, where it is burnt for 



