Mackinac Island State Park Commission, which is doing a commendable work of improvement and beautification and is maintaining and preserving the old buildings and military works of historical interest.

The geologic history of Mackinac Island is no less fascinating than its human history for there is recorded in the series of abandoned beaches, bars, spits, stacks, sea cliffs, and other shore features, a large part of the history of the ancestral Great Lakes. At the highest or Algonquin stage of the Great Lakes, Mackinac Island consisted of only a few acres of ground forming the highermost part now occupied by old Fort Holmes. As the waters of the ancient Great Lakes receded from their earlier shore lines and fell to lower and lower levels until the present stage was reached each successive lower stage was marked by its corresponding shore line features on the Island of Mackinac.

In the mapping and interpretation of these natural features of Mackinac Island the Geological Survey is not only doing an important. educational work but is also furthering the plan of the Mackinac Island State Park Commission to add to the interest and enjoyment of the several hundred thousand people who annually visit the island. During the summer season of 1914 field investigations were completed, and it is planned during the winter to construct a map of the Island on a rather large scale on which the geologic and physiographic features will be delineated, this map to be accompanied by a brief descriptive text. It is also planned to call attention to the meaning and interpretation of the natural features of the island through a system of guide posts and signs to be erected by the Mackinac Island State Park Commission. The work on Mackinac Island is in charge of Mr. Frank B. Taylor to whose indefatigable labors we are indebted for much of our present knowledge of the history of the Great Lakes."

I regret to state that Mr. Taylor's health has been such that he has been unable to complete his monograph, but it is expected that publication will be made before the end of another year.

GEOLOGICAL WORK.

The geological work accomplished during the biennium includes, (1) preparation and completion of a general geologic map of Michigan, (2) completion of investigations and report on Michigan commercial limestones, (3) continuation of field and laboratory studies of the pre-Cambrian rocks of the Northern Peninsula and preparation of a report covering these investigations in 1910-14, (4) completion of studies and preparation of a report in two volumes on the Devonian

formations of Michigan, (5) continuation of studies of the Mississippian formations, (6) preparation of a report on the physiography of the inland lakes, (7) current work in connection with publication of the annual report on mineral resources and statistics of mineral production and (8) miscellaneous investigations connected with correspondence and conferences.

A Geological Map of Michigan. I am pleased to report that a geological map of Michigan has been compiled and is now in the hands of the engraver and printer. Surprising as the statement may seem, it must be said that no adequate geological map of this state has ever been published. Certain parts of the state, particularly the iron and copper districts and a few counties, have been studied in detail and correspondingly accurate geological maps of these areas have been published. But for many years there has been a great need for a general geological map of the whole state representing in considerable detail the distribution and order of succession of the rock formations. We have had the compilation of such a map under way for several years but publication has been postponed pending study of certain districts in which information has been meagre or unastisfactory, particularly in the Northern Peninsula. There still remain certain areas in which the mapping is doubtful and others in which satisfactory differentiation between the formations of different ages is impossible. It is not deemed advisable, however, to longer delay the publication of a general map pending solution of doubtful questions of geology, some of which will require years of study. The map in its present form will be very useful, particularly in connection with an amply explanatory legend which accompanies it. This legend is an epitome of the geological history of the state and describes the different formations and their economic products in popular terms. The map will be especially valuable for instructional work in the schools and colleges of Michigan.

A Report on Michigan Limestone. Limestone is one of the important resources of Michigan. The production, particularly of the higher grades, is steadily increasing and will continue to increase as demanded in the expansion of the iron, chemical, paper and sugar industries. Michigan is peculiarly favored in the occurrence of extensive beds of high grade limestone on and near Lakes Huron and Michigan within reach by low cost transportation of the great limestone consuming industries of the Great Lakes region.

I am pleased to report that the investigation of the limestone resources of the state, which has been in progress since 1913 under charge of Mr. R. A. Smith, has been completed. Mr. Smith's report appears in Publication 21, Mineral Resources of Michigan. It was expected that

this report would be published in 1915 but it was found necessary to extend the investigations into 1916 to insure a thorough treatment of the entire subject. Mr. Smith has made a field examination of all of the districts and localities wherein limestone of commercial grade occurs, and has mapped the areas underlain, by commercial limestone in those regions to which development has not yet extended. The field investigations have been supplemented by thorough laboratory studies. In this work we have had the co-operation of all of the companies and individuals engaged in the Michigan limestone industry. Hundreds of drill records and thousands of limestone analyses have been supplied by the limestone operators. Without this co-operation the report would have been much less complete and valuable.

Studies of the pre-Cambrian Rocks of the Northern Peninsula. Field and laboratory studies of the pre-Cambrian rocks of the Northern Peninsula have been continued throughout the biennium. The main results of these investigations in 1910-14 have been summarized and published in Publication 18, Geological Series 15. During the summer of 1915 Mr. L. P. Barrett assisted by Messrs. Bela Hubbard, Don T. McKone, and Floyd B. Brown, were engaged in field mapping in the area between Gogebic Lake and the west end of the Marquette iron range. During the summer of 1916 these studies will be continued in the field by Mr. Barrett, in charge, assisted by O. R. Hamilton and Prof. I. D. Scott, geologists, and Messrs. Don T. McKone, James Tobin, and Joseph Hyde, compassmen. The area to be studied extends from the west end of the Marquette iron range westward and northward around the Huron Mountains, attention being mainly concentrated on the rocks of Huronian age and their relations to the overlying Keweenawan and underlying Archean terranes.

Studies of the Devonian Formations. During the biennium Dr. A. W. Grabau completed his studies on the Dundee, Traverse, and Antrim formations and has presented his report for publication. Dr. Grabau's work is an exhaustive treatment of the entire Devonian section and is abundantly illustrated, particularly the description of the faunal life of the Devonian seas. The work will be published in two volumes during the next biennium as the second of a series of monographs on the Paleozoic formations of the state.

Studies of the Mississippian Formations. Under a co-operative arrangement with the United States Geological Survey Dr. Geo. H. Girty, Paleontologist, has continued his studies of the Mississippian, comprising the formations known as the Coldwater shale and Marshall sandstone. Up to this time Dr. Girty's studies have been mainly

concentrated on the Marshall fauna and his report on this formation is almost completed. During the summer of 1915 Mr. George M. Ehlers was employed in field examinations of the Mississippian and the collection of fossils from its exposures under the supervision of Dr. Girty. It is probable that some additional collections will need to be made from the Coldwater formation.

Studies of the Paleozoic Formations of the Northern Peninsula. Our knowledge of the lower Paleozoic formations which form the Northern Peninsula east of a line from Marquette to Menominee is unsatisfactory. It is based on early observations of Houghton, Winchell, and Rominger supplemented by later somewhat cursory study by A. C. Lane and others. This area connects the much more studied and better known areas of correlative formations in Ontario and New York on the east and Wisconsin on the west and the solution of a number of important problems awaits a comprehensive invest gation of the Michigan section. It would hardly be worth while to undertake a study of this large area except under a general plan providing for several years continuous field and laboratory studies by competent straitgraphers and paleontologists. Such a plan is under consideration. Pending the formulation of a definite program for this work Mr. Geo. M. Ehlers has been employed to make extensive fossil collections and general field study of the Niagaran formations during the summer of 1916 under the supervision of Prof. E. C. Case and R. A. Smith.

A Study of the Physiography of Michigan Inland Lakes. In my last biennial report a full account was made of the work of Dr. I. D. Scott on the physiography of Michigan inland lakes. Dr. Scott has had the preparation of a report on this subject under way during the biennium and should be able to finish it before the end of the present year.

The report will consist of two parts. Part 1 is intended to familiarize the lay reader with the manner of formation of lake basins, the forces which are active on the shores, the effects of these forces, and the processes through which lakes eventually become extinct. It includes a general statement of the topography of Michigan, a brief discussion of the work of running water and glaciers, a classification of lake basins and the manner of formation of the types found in this state, a statement of the work of waves, currents and ice and the resultant forms. Part 2 will contain descriptions of the shores of the various lakes treated individually. The pysiographic forms and the manner of their formation will be discussed together with an account of the origin of the basin and the factors working towards the extinction of the lake.

Mineral Resources and Statistics. The annual report on statistics of production and progress of the mineral industries is one of the most generally useful and popular publications of the Survey. In this work we have the indispensable co-operation of the mineral producers as well as that of the United States Geological Survey. In addition to the statistical matter this report contains a directory of all of the mineral producers, statements of progress of the industries and each year a leading article on one of the mineral resources. The report for 1914 contains a very useful treatment of the copper deposits by Mr. R. E. Hore, the report for 1915 a valuable contribution on Michigan commercial limestones by Mr. R. A. Smith.