388 TJie American Geologist. December, 1900 
The method of Michel Levy presents at a glance a clear 
conception of the whole chemical character of the rock with 
indications, nearly always quite precise, as to the mineralogical 
composition. It permits a ready reconstruction of the full 
chemical composition* of the rock from the diagram 
itself. One of its important points of superiority is the clear- 
ness with which the various ratios between the oxides appear. 
It separates the feldspathisable calcium oxide from that enter- 
ing into the ferromagnesian minerals, and if an excess of 
either alumina or sodium oxide occurs it is brought out with 
remarkable clearness. 
{Concluded.) 
METEOROLOGY OF THE ORDOVICIAN. 
By F. W. Sardeson, University of Minnesota. 
Meteorologic conditions in the Ordovician time are to be 
considered apparently as nearly indeterminable because of in- 
sufficiency and indirectness of evidence. One may of course 
say that the Ordovician had pre-Carboniferous climatic con- 
ditions, or even that the Ordovician is to the Carboniferous as 
the Carboniferous is to Recent climate, which however, means 
nothing definite if we are not agreed on the Carboniferous con- 
ditions. In such a state of knowledge upon an important sub- 
ject, any direct evidence, however slight may be welcomed in 
printed form, and therefore the following is offered. 
What may be considered as direct evidence on the subject 
is found in a fossil of the Monticuliporoidea which occurs in 
the Ordovician, and which winds at least simulating heliotrop- 
ism. Rhinidictya mutabilis Ulr., is found fossil as more or less 
broken parts of a zoarium which when reconstructed may be 
described as follows : It grew attached to the sea bottom by a 
small basal expansion from the center of which rose a dich- 
otomously branching calcareous skeleton to the hight of 100 
mm or less. The growth was at the branch ends mainly, the 
branches thickening very slowly below these points. The 
whole zoarium resembles a sea weed in habit, although in fact 
*With the exception, of course, of such elements as TiOs, P2O5 
H.O, CO., etc. 
