230 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



later years of the survey, but it will be none the less inter- 

 esting on that account. 



The state was not regularly divided into districts, but the 

 least-known portions were surveyed first. Five district sur- 

 veys were organized: one in the azoic rocks; one in the 

 Lower Silurian iron -ore limestone belt; one in the Upper 

 Silurian fossil-ore belt, taking in the ore belt of the Lower 

 Devonian ; one in the oil - field, and one in the bituminous 

 coal -field. Afterwards two other districts were occupied 

 one that of the Chemung rocks of the northern counties, and 

 another in the bituminous coal-field. 



Gradually the number of independent assistant geologists 

 was increased, so that in 1877 Professor Stevenson, Professor 

 White, Mr. W. G. Piatt, and Mr. Ashburner have surveyed 

 separate parts of the bituminous -coal area. Mr. Carll and 

 Mr. Chance have together continued the survey of the oil 

 region. Mr. Sherwood has made colored outcrop maps of 

 three northern counties, in addition to three previously made; 

 Air. Franklin Piatt has finished Blair County; Mr. Chance has 

 finished a large contour-line map of the Upper Juniata lime- 

 stone region ; Mr. Billin has half finished a large contour-line 

 map of the Buffalo mountains; Mr. Sanders has nearly half 

 finished the contour-line map of the South Mountain range; 

 Mr. Berlin, under the direction of Professor Prime, has finish- 

 ed the limestone belt iron-ore map as far west as Reading, 

 and commenced the contours of the mountains between the 

 Delaware and Schuylkill rivers; Professor Frazer has finish- 

 ed a survey of Lancaster County; Mr. Sanders has laid in 

 the outcrops of Cumberland County, and Mr. C. E. Hall and 

 Mr. Fellows have made large collections and traced outcrops 

 along the Philadelphia belt of azoic rocks. 



No changes have been made in the personnel of the corps 

 since its organization. The work is harmonious, the mem- 

 bers zealous, and the results large some of them new and 

 unexpected; but in the main the accuracy of the old survey 

 of 1835-41, under the brothers Rogers, has been satisfacto- 

 rily established. 



The function of the new survey is one of differentiation 

 and precision. The contour -line maps, on a large scale, 

 based on a reticulation of transit and level work, are its best 

 illustration. A multitude of connected, measured, vertical 



