42 
IKON—QUARTZ—JASPER. 
be seen on the road to Goosevvell near Plymstock, 
and in other spots. Occasionally also, ordinary 
slate assumes a very indurated aspect, without al¬ 
tering its colour or general qualities, this may be 
observed on the Exeter road just beyond Elburton. 
Iron is found in some parts of our slate in loads, 
and also is scattered in mere traces, through the 
substance of nearly all our rocks of this formation, 
appearing in slight indications in the schist adjoin¬ 
ing those few beds of this metal which occur in 
limestone ; it occasionally betrays itself in small 
insignificant masses of sulphuret. Quartz pervades 
it most freely in some places, and these narrow veins 
seem invariably to end in points. At Compton is a 
pretty large vein o f jasper, much mixed with ordi¬ 
nary quartz ; I have seen many small blocks from 
thence. Jasper is also often found on Roborough 
Down, among heaps of ordinary stone used for 
repair of roads. 
The prejudices and prepossessions of geologists, 
appear far more hastily formed and more deeply- 
rooted than those of any other kind of philosophers, 
and because involving so long a train of consequen¬ 
ces, far more prejudicial, and far more inexcusable. 
Until the recent set of geologists turned their atten¬ 
tion to the science, it consisted of theory , now it 
mostly consists of facts. The slate of South Devon 
had all along been condemned as non-fossiliferous, 
and though the limestone has for some time been 
admitted to contain reliques, it is only lately, that 
slate has been characterised by a lecturer at the 
Plymouthlnstitution, as destitute of animal remains.* 
* See Mr. Walker’s “ Lecture on Geology.” Also Mr. Prideaux 
on “ Geology of South Devon,” who considers the Cann slate 
“ primitive .” Also" Guide to the Watering Places,” by Turton 
and Kingston, where the slate of that district is said to be devoid 
of fossils, though at Brixham they are found in vast abundance— 
Turbinoliue, Encrinites, &c. 
