474 The American Naturalist. [May, 
filling interstices between its crystals. The authoris inclined to regard 
the ore as having separated from the rock magma, but, whether in 
accordance with the Soret principle, or not, he is unwilling to say. 
A variolite in a small dyke at Dunmore Head, County Down, Ire- 
land, is described by Cole” as an altered glass containing spherulites 
composed of cryptocrystalline material with a delicately radial struc- 
ture. Cracks traverse the spherulites and also the groundmass of the 
rocks. Into some of those in the spherulites glass has been forced. 
Occasionally the nuclei of spherulites are crystals of plagioclase. 
In a general geological article on the Essex and Willsboro’ Town- 
ships in Essex Co., N. Y., White” records the existence of a number of 
bostonite, fourchite, camptonite and other dykes cutting the country 
rocks of the region. 
GEOLOGY AND PALEONTOLOGY. 
The Lakes of Central Africa.—Concerning the origin of the 
Central African lakes, Dr. D. Kerr-Cross advances the theory that 
these lakes were in the first instance, arms of the sea, as the Red Sea 
is at the present time. During Cenozoic time the whole continent 
participated in a general movement resulting in the crushing, subsid- 
ence, faulting, and upheaval which are evident on every hand. The 
fauna living on during these successive changes has gradually adapted 
itself to the varying environment. This theory is founded on the fol- 
lowing facts collated from the author’s own observations, and those of 
other East African travelers : 
1. East Africa is a country of table-lands. 
2. Its lakes, Tanganyika, Nyasa, Rulswa, Bangweolo, Newero, and 
to some extent those further north—not to speak of the lesser lakes— 
run more or less in the lie of the continent north and south, and are 
separated from the sea to the east by highland, and are environed by 
great mountain systems remote from those of the coast range. 
3. The lakes are all at high elevation. 
4. Some of the lakes have evidence of great volcanic activity having 
taken place in late geological time. There are recently extinct 
craters, and hot springs and lava flows. 
Geol. Magazine, April, 1894, p. 220. 
. Y. Acad. Sci., xiii, p. 214. 
