642 DIORITES OF THE WARWICKSHIRE COAL-FIELD. 
able way suddenly changed about the commencement of the Tertiary 
eriod. 
It may be observed in conclusion that these Warwickshire rocks 
differ greatly from the neighbouring syenites of Leicestershire, re- 
cently described by Professor Bonney*, with which I am also well 
acquainted. In the latter the prevailing felspar is orthoclase, and 
quartz is always present; epidote is also a very common secondary 
constituent. I have detected no trace of either quartz or epidote in 
the diorites, and orthoclase invariably occupies a very subordinate 
position, 
* Quart. Journ. Geol. Soc. vol. xxxiv. p. 225. 
