xii PREFACE. 



ical work proper of the survey has always thus far required the full amount of time 

 and means that were available; second, that the knowledge necessary for thorough 

 scientific work in this direction could not be easily commanded. In short, it may 

 be true that the time has not yet come for a satisfactory treatment of the important 

 relations between geology and agriculture, but the subject is to be kept in view as 

 one of the unfinished problems of the survey. A beginning could perhaps be made 

 with profit at the present time in a preliminary classification of the soils of the 

 State in connection with their native floras. Such a task would require adequate 

 acquaintance with and adequate interest in the several branches involved which in- 

 clude agriculture, botany, meteorology, geology, chemistry and some divisions of 

 zoology. 



The building-stones of the State have not received the attention that their 

 growing importance demands. No review has been made of them since the publi- 

 cation of volume V, and the treatment at that time was far from satisfactory, hav- 

 ing been condensed from a report made for the 10th United States census. A good 

 beginning of a new chapter on this subject was made four years since by the writer 

 but the loss of the field no'tes before they were put in shape brought this purpose to 

 naught. 



The recent discovery of rock salt in northern Ohio and the establishment of an 

 important business upon this unexpected occurrence have been alluded to in the 

 opening chapter of the present volume, but the facts justify a more extended 

 account for which, to my regret, time and space do not now suffice. 



The production of petroleum and gas has been by far the most interesting and 

 important subject in the economic geology of the State during the last ten years. 

 Three separate volumes of the Survey reports have been devoted almost exclusively 

 to it within this period, viz.: Preliminary Report, 1886, Vol VI, 1888, and First 

 Annual Report, 1890. The development has gone on with unabated vigor since the 

 publication of the last volume and a rich harvest of facts remains uugarnered at 

 this time, but the exclusive privileges of this subject could not be further continued 

 without doing injustice to other economic interests. I greatly regret that I have not 

 been able to follow with proper care and detail the progress of the drill during the 

 last four years. I also regret that the want of space forbids the introduction of such 

 of these facts as I have in hand into the present volume. 



Two oil fields of considerable importance have been brought to light within 

 this time, viz.: The Monroe county and the Corning fields. 



The Monroe county oil is derived from the Logan Conglomerate which is known 

 in the adjacent Sistersville oil field of West Virginia as the " Big Indian" sand. It 

 is identical with the salt water rock of Pomeroy, and also with the great salt water 

 horizon of the Macksburg oil field. Its outcrops constitute the most striking 

 feature in the scenery of the Hocking Valley from Lancaster to Logan and are also 

 finely shown in the picturesque gorge of the Licking river between Newark and 

 Zanesville. 



The Corning field derives its oil from, the Berea Grit, which is reached in wells 

 about 1,000 feet in depth. These wells produce a moderate quantity of rather heavy 

 oil but they seem to show fair vitality. 



The principal feature of the last four years in this connection is, however, the 

 continued development and expansion of the oil production of the Trenton lime- 

 stone in northwestern Ohio. Tfiis production is beyond question the most striking 

 and suiprising fact in the economic geology of the country for the last twenty-five 

 years. Ten years ago, it would not have been possible to make a more improbable 

 forecast as to the future oil supply of the country than one which should embody 

 the results of our present experience. The black swamp of northwestern Ohio is at 

 this time the leading source of the illuminating oil of the United States and the 

 source of this oil is found in a lower Silurian limestone. 



