12 
GEOLOGICAL REPORT-THIRTY-FIFTH PARALLEL. 
metamorphic slates were seen two and a half miles above the first outcrop, but their height 
above the river does not exceed ten to thirty feet ; and, again, four miles above, the slates were 
seen supporting strata of sandstone of carboniferous age in an unconformable position. Thus, 
as Mr. Marcou observes, the uplift of the metamorphic schists appears to have been anterior to 
the deposition of the sandstone. I find on the maps of Arkansas a range of mountains indicated 
directly west of Little Rock, called the Washita mountains. They have an east and west 
tre:.d, and are parallel with the line of elevations upon which Little Jean mountain is situated, 
end which will he presently referred to. It is probable, therefore, that the ridge of Little Rock 
is a continuation of this east and west line of elevation. Mr. Marcou (see notes) states, also, 
that a line of hills commence at that point, hut they do not reach an elevation of more than 100 
feet. 
The formations of Little Rock were examined by Featherstonhaugh as early as 1834, and 
were described by him in his report as “ grauwacke,” and he considered it as the equivalent of 
that of the English geologists. He observes: “The grauwacke slate here is highly inclined, 
and, dippingS. by E., is traversed by very broad hands of quartz ; no red sandstone is super¬ 
imposed upon it at the river, hut at a very limited locality on the hank I found a calcareous 
deposite containing marine fossil shells belonging to the Tertiary beds.” 1 These fossils are said 
to be of the genera Ostrea , Turritctta, Calyptrea , and Cerithium. The same deposite is said to 
he found three miles farther west in considerable quantities, and it was quarried there for 
making lime. The same writer observes, respecting the “old-red sandstone,” (probably the 
Carboniferous,) that it forms ridges at a distance of about five miles from the town, which trend 
about east and west. “ The Mammelle mountain, distant about eighteen miles from Little Rock, 
is an outlier of the same formation.” “ The southwest aspect of the cone is very imposing, and 
bears a strong resemblance to a pyramid ; on approaching it, the whole facade presented a 
lofty mural escarpment, about seven hundred feet above the level of the Arkansas river, accord- 
PETIT JEAN MOUNTAIN. 
ing to the computation I was able to make, with a broad talus at the bottom.” “ The southwest 
edge of this pyramid showed the truncated beds of the rock standing at an elevation of 75°, 
and in some places they were vertical.” 2 
These elevated bluffs of the carboniferous formation are numerous in that region. One of the 
1 Report on the elevated country between the Missouri and Red rivers, pp. 59, 60. 
Ibid., p. 60. 
