ILLUSTRATIONS Facing Plate I. Index map of northeastern Maryland showing the positions of plates giving the location of feldspar quarries........ page 96 .... 104 II. Location of feldspar quarries in Cecil and Harford counties show- ... ..... 112 ..... 120 IV. Location of feldspar quarries in part of Baltimore County and in Carroll and Howard counties..... V. Map showing the locations of present and past flint mills, and posi tions of plates giving location of flint quarries... 128 VI. Location of flint quarries in part of Harford County... VII. Location of flint quarries in part of Baltimore, Carroll, and Howard counties... 136 144 152 VIII. View of Annapolis Rock White Flint deposit.... IX. Map of northeastern Maryland showing areas of serpentine rock and position of maps giving location of localities at which chrome ores have been produced.... 160 176 X. Map of a portion of Cecil County showing serpentine areas and localities at which chrome ores have been produced............. 168 XI. Map of a portion of Harford County showing serpentine areas and localities at which chrome ores have been produced...... XII. Map of portions of Baltimore County showing serpentine areas and localities at which chrome ores have been produced......... 184 XIII. Map of a portion of Montgomery County showing locality at which chrome ores were mined.... 192 XIV. Fig. 1.—View of serpentine quarry and saw-mill at Cardiff 1901... 256 Fig. 2.-View of serpentine quarry at Cardiff 1928... 256 XV. Fig. 1.-View of serpentine barrens at Broad Creek.. 264 Fig. 2.-View of serpentine barrens at Soldiers Delight....... XVI. Map showing serpentine areas in Harford County and rock specimen numbers.... 264 280 Figure Page 1. Profile of Pleistocene terraces showing deposition of molding sand 44 166 3. Screen analysis curves of five sand chrome samples showing percentage of each mesh size..... 169 4. Screen analysis curves of five sand chrome samples showing percentage above indicated mesh size.... 169 Figure Page 5. Screen analysis of magnetic and non-magnetic portions of Sample I. 170 6. Screen analysis of magnetic and non-magnetic portions of Sample IV........ 7. Sketch of surface workings of the Reed Mine... 173 181 8. Textures of serpentine formed by the alteration of 1. olivine, 2. amphibole, and 3. pyroxene respectively..... 247 9. Figure showing central cleavage lines of serpentine surrounded by magnesite.... 275 PREFACE The present volume is the twelfth in the series of General Reports issued by the Survey at irregular intervals which contain shorter papers and reports of more general interest. The monographic treatises on the major geological divisions are issued as a second series of Systematic Reports; while the more detailed reports, chiefly of local interest, are issued as a series of County Reports. The papers of the present volume represent the results of studies made at different times, some of them years ago, which have been available for consultation in the office but are now presented in permanent form for more general use. Part I. The Molding Sands of Maryland, by David W. Trainer, Jr., is one of a series of studies conducted in coöperation with various agencies to determine the national resources in this commodity so essential to many industries. The report gives the properties of actual or supposed molding sands from many localities in southern Maryland and shows that the State possesses deposits which may lead to the development of a molding-sand industry. The author shows that the most favorable occurrences are near the base of the Sunderland terrace and suggests a reason for their formation at this location. Part II. Notes on Feldspar, Quartz, Chrome, and Manganese in Maryland, by Joseph T. Singewald, Jr., are a series of short papers on the materials named. Most of the deposits are small and situated in the crystalline rocks of northern Maryland. The author has described many of these small quarries or temporary openings and discussed the annual production during the last ten years. Although the values are not large the State has been a steady contributor of feldspar and flint for many years. The annual production of chrome in Maryland at the present time seldom exceeds 100 long tons but a century ago the State was one of the chief producers in the world and the discovery of chromite by Isaac Tyson Jr. was the cause of establishing one of the best known industries in Maryland-the Chrome Works-which is still active in refining foreign ores. The uses and demands for chrome are constantly increasing but Maryland deposits cannot compete successfully with the larger and richer deposits elsewhere. Manganese has been found at several points in the State but attempts to develop these deposits have so far been unsuccessful. The work done, while giving no indications of large deposits, was not sufficient to demonstrate that such bodies did not exist. Part III. The Serpentines of Harford County, Maryland, by Albert Johannsen represents work done by the author many years ago when he prepared the manuscript for the present publication. Terminologies and viewpoints in the subject have changed somewhat since this report was written and papers written today would lay somewhat different emphasis on the points discussed. The facts given in the report have been available for the use of the Survey for years and the field studies of the author have been used extensively in previous publications of the Survey. Part IV. The Gabbros and Associated Intrusive Rocks of Harford County, by Herbert Insley is a second manuscript based on field work done some years ago during the survey of Harford County. The author presents the results of a scientific investigation of one of the more extensive rock formations of the county which is never likely to be of greater commercial importance than for road metal and railroad ballast. Large quarries have been opened along the Susquehanna and thousands of tons of these rocks are being used in the manner indicated. |