476 PROFESSOR GEIKIE ON THE 
found in the manner in which they catch up and completely enclose portions 
of the underlying or overlying strata. The well-known examples on 
Salisbury Crags (fig. 18) are paralleled by scores of other instances in different 
parts of the region. The subjoined woodcut (fig. 
19) represents the way in which an intrusive sheet 
of a pale much altered rock involves shales in the 
Edinburgh district. 
Moreover, the sheets do not always remain on the © 
same horizon; that is, between the same strata. They 
may be observed to steal across or break through the 
beds so as to lie successively between different layers. 
No more instructive example of this relation could be ~ 
cited than that of the intrusive rock which has been 
Fig, 18.—Intrusive dolerite sheet laid open in the Dodhead Limestone Quarry, near 
enclosing and sending threads into ‘ ‘ ; 
portions of shale, Salisbury Crags, Burntisland. As shown in the accompanying figure 
Hainbangh. (fig. 20) this rock breaks through the limestone and 
then spreads out among the overlying shales, across which it passes obliquely. 
But when we trace the larger intrusive sheets this transgressive character is seen 
Ge Ewe N me 
ae Bross By 
ee Fee 
Yee A ee LT 
Fig. 19.—Intrusive sheet enveloping shales. Bed of Linhouse Water. 
“Geol. Survey Memoir of Edinburgh District,” p. 115. 
Ne et te pe Uae haa SNH 
the ol ess 
fun From, Paw Wey, 4 eS 
et 1”, Any Ping 1 
== <5: 
LAAN cp TONY 
wee 
yey, Wer Nida 
aes = 
Fig. 20.—Intrusive sheet invading limestone and shale, Dodhead One near Burntisland. 
to be sometimes manifested on a great scale. Thus, along the important be 
of intrusive rocks that runs from Kilsyth to Stirling, the Hurlet limestone hes 
