ON THE TRAP-ROCKS IN YORKSHIRE, 8cc. 479 
the south of the above described boundaries. They con- 
sider it as perfectly stratified, and estimate its depth from 
12 to 18 fathoms. The extent of this field of trap is of 
prodigious magnitude. Its length from N. to S. must 
exceed 70 miles, and in many situations its breadth is from 
12 to .15 miles. 
From wliat source this great trap-range is to be traced, 
is a subject upon which the most highly enlightened geolo- 
gists, mineralogists, and chemists, are as yet at variance. 
By some it is believed that this immense mass of greenstone 
has been poured out from that singularly extensive and 
curious whin-dike (commonly called the Bolam, or York- 
shire Dike), which may be seen marked in all the geologi- 
cal maps. It may be distinctly traced from the German 
Ocean, near Whitby, a distance of above 70 miles, into the 
field under consideration. By others, it is contended, that 
it is the production of a vast volcanic eruption from the al- 
pine chain at its head. To others, again, there appear strong 
reasons to suspect either of these possibilities: 1^^, The 
source from which it is supposed to flow, is not known to 
contain any metallic ores ; 2dli/j The substance in this great 
extent appears to have no tendency to vesicular conci'e- 
tions, or any vitreous appearance ; and, Sdit/, Its regular 
stratification for so great a distance, induces belief, that its 
formation has been in contemporaneous succession with the 
various strata forming the successive and curious alterna- 
tions in this interesting district of the lead-measures. 
The vast extent of this mass of trap or greenstone, its 
stratification^ its veins of galena, its relations with the 
neighbouring strata, render it highly deserving of the at- 
tention of the geologist and the miner. 
The present notice, although very imperfect, will, I 
trust, lead to a farther examination of the trap-rocks of 
