GEOLOGY. 293 



long duration ; then a second diluvial period, without great glaciers, 

 and to which the diluvial cones belong ; then, lastly, the modern period 

 represented by the modern cone or delta. This succession of events, 

 in the opinion of M. Morlot, establishes a duration of about 1,000 

 centuries at least for the last geological epoch, which began immedi- 

 ately after the retreat of the hist great glaciers, which was character- 

 ized by the presence, of the Elcpltas priinitjennix and by the appear- 

 ance of man, and which ended at the beginning of the modern period, 

 the latter having already lasted, in his opinion, about 100 centuries. 



FACTS ABOUT PETROLEUM. 



The development of the business of obtaining petroleum in this 

 country has progressed during the past year with wonderful rapidity ; so 

 much so indeed that the business itself is now recognized as one of the 

 greatest and most lucrative branches of American industry. Respecting 

 the origin of the petroleum, its geological relations, and its industrial 

 applications and treatment, few facts additional to those already given 

 in the previous volumes of the Annual of Scientific Discovery have 

 been made known. Many new localities productive of oil have, how- 

 ever, been discovered ; and it is the opinion of some geologists who 

 have given the subject attention, that the geographical area covered 

 by oil-bearing rocks on the North American Continent east of the 

 Mississippi, cannot be less than 200,000 square miles. Springs 

 yielding petroleum in immense quantities are also reported by Prof. 

 Silliman and others, as existing upon the Pacific coast. 



We derive the following particulars respecting the present produc- 

 tion of petroleum in the oil-districts of Pennsylvania, mainly from the 

 correspondence of the New York World: 



The average depth at which oil is found by boring is from 550 to 

 600 feet ; in some instances, however, the wells exceed 700 feet in 

 depth. Oil is not always obtained at once, but many of the best wells 

 have to be pumped for days or weeks, before they commence flowing. 

 All flowing wells, moreover, do not flow continuously, and some of 

 the phenomena presented are highly interesting. Thus, for example, 

 the so-called "Yankee Well" located on Cherry Run, was sunk in 

 July, 1864, and is 606 feet deep. After being pumped two weeks, 

 the* well yielded, by pumping, from ten to twenty barrels per day. 

 Afterwards, just as the workmen had started to pull the tubing for the 

 purpose of improving it, oil commenced to flow without pumping, at 

 the rate of thirty-five barrels, increasing at last to fifty barrels per day. 

 The flow is spasmodic, lasting from five to seven minutes. The time 

 of flow and the interval of quiet rarely vary over one or two minutes, 

 then ceasing for about 20 minutes. 



Another well, the " Gruniger," in the same district, 600 feet deep, 

 first yielded, in September, 1864, by pumping, fifty barrels per day. 

 It subsequently began flowing without the aid of a pump, from filty to 

 sixty barrels, increasing gradually to a hundred and fifty barrels per 

 day*. It is now flowing about a hundred barrels, the flow being also 

 spasmodic, from three to five minutes duration, commencing every 

 twelve minutes. Other wells flow once in a half hour, and some only 

 once and for a short period in several days. 



The following is a summary of the result of operations in February, 



