26 TRANSACTIONS OF THE [NOV. 26, 
form the middle member of the Cretaceous system, between the 
Dakota series below and the Laramie above. In the Upper 
Missouri region, this middle portion was subdivided into several 
members, in the well-known classification of Meek and Hayden ; 
but these divisions are comparatively local, and in Colorado all 
have been united as one great middle series. Their relation is 
best seen .in the N.W. angle of the State, near Glenwood Springs. 
Here the strata have been steeply tilted, and present the follow- 
ing succession in a length of some four or five miles across the 
valley of Grand River : 
1. Granite. 
2. Potsdam sandstone. 300 feet thick. 
3. Palseozoic limestones. SOO KES Os 
4. Triassic. 25000) jo" tne 
5. Jurassic. 500m ee Te 
6. Cretaceous, Dakota series. 310 BMF ea 
iG Ge Colorado shales. 2000 ‘* = * 
8. es Laramie series. 3000 ‘* ‘*‘ 
The oil has a pleasant ethereal odor, quite different from that 
of the Pennsylvania oils, and more like those of Italy. When 
crude, it has a density of 31° B., and is refined and deodorized 
with great ease, yielding 40 per cent of very clear and beautiful 
oil. A large amount of paraffin is left in the residuum, which 
makes an unequalled lubricant, and would be valuable for that 
purpose in Hastern markets. The company, however, employ it 
as fuel in their works, for which purpose it is admirable, but in 
reality costly. 
As regards the geological question of the origin of petroleum, 
there can be no uncertainty. It is always found in association 
with bituminous shales or limestones, and is plainly a product of 
partial distillation from organic matter, chiefly vegetable. If 
the process goes on further, we have, as the result, the various 
forms of natural tar, asphalt, ozokerite, bitumen, albertite, 
grahamite, etc., by a gradual lossof volatile matter and increase 
in the percentage of carbon. Precisely in the same way, in the 
coal-series, we pass, by well-known steps, from vegetable fibre 
through peat, lignite, etc., to the soft or bituminous coals, and 
from these likewise to the anthracite coals, and finally to graphite. 
Bituminous coals left exposed to the weather frequently lose 
their volatile matter, and become worthless for gas-making, 
much as these bituminous shales are constantly discharging it, 
and giving rise to gas-wells and oil-wells as the result. The 
further transition from oil to asphalt may be seen now in some 
places, e. g., in the great pitch-lake on the island of Trinidad. 
At many points, it is evident that hard asphalts and asphaltic 
