120 
LACCOLITHIC STRUCTURES 
Feet 
8. Quarternaric loams and gravels. 200 
7. Tertic marls and sands. 1500 
6. Mesa Verde shales and sandstones. 800 
5. Montana shales. 500 
4. Colorado shales. 1200 
3. Mora sandstones (Cretacic). 500 
2. Carbonic limestones. 2500 
1. Proterozoic schists. 4000 
The close association of the Carbonic limestones and the Cre¬ 
tacic formations in this region appears due mainly to the fact 
that a great unconformity exists, permitting the latter often to 
repose directly upon the former. 
The thickness of the strata overlying the uppermost of the 
Ortiz sills could not have been in any case, when the intrusion 
took place, more than over 2,000 feet; or 3,000 feet even if the 
intrusion is regarded as having taken place in the lower (Mon¬ 
tana) section. Since the intrusion doubtless occured in Early 
Tertic time probably not one-half of the known Tertic deposits of 
the region was yet laid down. A thickness of 2,000 feet of sedi¬ 
ments would in all likelihood be nearer fact for the actual volume 
of strata floated upward in the formation of the Ortiz laccolith. 
Tuertos laccolith, on which the San Pedro contact copper de¬ 
posits are situated, is similar in all respect to the Ortiz Moun¬ 
tains. The geological horizon of the intrusion appears to be the 
same and the Montana sandstones and shales are upturned on 
the eastern flank of the mountains. The Carbonic limestones, on 
the west side in the vicinity of San Pedro, seem to be elevated 
and tilted on account of faulting. In any case, 3,000 feet of 
covering when the contact deposits were formed would be, so far 
as present evidence goes, a maximum. Taking into considera¬ 
tion the character of the rocks this figure is barely one-tenth of 
the thickness required to bring the horizon within the zone of 
rock-flowage. 
