336 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
of the Elkton shaft, turns rather sharply to the south-southwest and soon pinches 
out. Fifty feet farther west another basalt dike is cut, which continues southward 
through the western edge of the plionolite laccolith and into the granite near the 
Thompson shaft. Many other examples might be cited illustrative of this tend¬ 
ency of the Raven-Elkton dike, but it is a feature so characteristic of the basaltic 
dikes of the district as to render unnecessary detailed reference to each case. 
Although portions of the dike are hard and fairly fresh, it is usually rather soft 
and decomposed and breaks up upon exposure to the air. As a rule it is traversed 
by numerous fine cracks, generally parallel with the plane of the dike and particu¬ 
larly abundant near the walls. As in the Portland, some of these cracks are filled 
with veinlets of calcite. In general, however, this platy structure of the dike is 
much less conspicuous than the sheeting of the adjacent breccia. It has less the 
appearance of sheeting produced by external stresses than of originally incipient 
cracks due to the cooling of the basaltic magma and rendered visible by later alter¬ 
ation. This contrast, as well as the way in which the Raven dike turns and fol¬ 
lows the Walter sheeting zone, strongly suggests that the main sheeting of the 
breccia, granite, and plionolite occurred before the intrusion of the basalt, though, 
as will presently be shown, the mineralization is certainly mainly post-basaltic. 
This was clearly the conclusion reached by Penrose/' who writes: 
In fact the dike seems to have been originally intruded into a much-fissured zone and to have come up 
along slightly different lines even in local areas. In several places, also, it forks and follows two diverging 
fissures, though one branch usually comes quickly to an end. The zone of Assuring occupied by the dike and 
that occupied by the [Raven] vein represent different lines of fracture and cross each other at low angles; 
but both fissures were formed before the intrusion of the dike, as is shown by the fact that at the crossing of 
the fissures near the Raven shaft the dike throws out a fork for a few feet from the main dike along the vein 
fissure, thus clearly proving its later age. 
The so-called Catherine dike, noted by Penrose 6 on level 1 of the Elkton and 
supposed by him to be older than the Raven dike, could not be found on the levels 
now accessible and was probably merely a local offshoot from the Raven dike 
along the sheeted zone of the Walter lode. 
FORM AND STRUCTURE OF THE ORE BODIES. 
The important Elkton ore bodies fall into three general classes—first, distinct 
lodes, following either the “basalt” dike or well-defined sheeted zones; second, 
irregular bodies in granite largely due to metasomatic replacement; and, third, 
the peculiar “flat” ore bodies on level 7 between the Elkton and Thompson shafts. 
The main Walter pay shoot has a maximum length of about 1,700 feet and 
with the exception of a few low-grade portions has been stuped continuously from 
the Elkton to the Tornado shaft and from level 7 to the surface. North of the 
Tornado shaft relatively little ore has been found, the north end of the main Walter 
pay shoot practically coinciding with the southwest contact of the Tornado phono- 
lite dike. From the collar of the Elkton shaft the southern limit of the Walter ore 
body pitches south to a point on level 4 about 350 feet south of the shaft. It 
thence pitches north until, on level 7, the south end of the Walter pay shoot proper 
is again at the Elkton shaft. There are, however, below level 6 isolated pay shoots 
a Sixteenth Ann. Rept. U. S. Geol. Survey, pt. 2, 1895, pp. 181-182. 
b Op. cit., p. 185. 
