PREFACE. This, the first edition of the rearranged H. O. Publications No. 108-A, 108-B, and 108-C, contains descriptions of and sailing directions for the Detroit River above the city of Detroit, Lake St. Clair, St. Clair River, Lake Huron, Georgian Bay, North Channel, Lake Michigan, and Lake Superior. The information embodied in this publication is mainly from Canadian Sailing Directions, for the Canadian shores of Lake Huron and Georgian Bay, H. O. Publications 108-A, 108-B, and 108-C, Bulletin No. 29, by United States Lake Survey Office, H. O. Charts, Lake Survey Charts, and Canadian Charts. It is corrected through Notices to Mariners No. 8, 1921. The bearings and courses are given in degrees true, to the nearest degree, followed by the equivalent magnetic bearing. expressed in points to the nearest point, in parenthesis, thus with a variation of 5° west, course north true would read 0° (N E). Bearings limiting the sectors of lights are toward the light. The directions of winds refer to the points from which they blow; of currents, toward which they set. These directions are true. Variations for the year, with the annual rate of change, may be obtained from Lake Survey Chart No. 0. Distances are expressed in statute miles, the mile being approximately 1,760 yards. Heights are referred to mean lake level. For all details of lights and fog signals, the mariner should consult Light List, Great Lakes, United States and Canadian, issued by the Lighthouse Bureau of the Department of Commerce. Depths. The datum for the soundings mentioned herein are as follows: The depths for the Detroit River are referred to the sloping surface of the river corresponding to a Lake St. Clair stage of 573.8 feet and a Lake Erie stage of 570.8 feet above mean sea level. The depths for Lake St. Clair herein given are referred to lowwater datum, the reference plane for United States river and harbor improvements, which for Lake St. Clair is 573.8 feet above mean sea level. Depths on the Lake Survey Charts referred to 575.11 feet above sea level are 1 to 13 feet more than those given herein. The depths for the St. Clair River are referred to the sloping surface of the river corresponding to a Lake St. Clair stage of 573.8 feet and a Lake Huron stage of 579.6 feet above mean sea level. The depths for Lake Huron herein given are referred to lowwater datum, the reference plane for United States river and harbor improvements, which for Lake Huron is an elevation of 579.6 feet above mean sea level. Depths on the Lake Survey charts, referred to standard low water, are generally 1 foot less than those published herein. The data of the soundings for Georgian Bay and North Channel are given at the beginning of each chapter. The depths for Lake Michigan herein given are referred to low water datum, the reference plane for United States river and harbor improvements which for Lake Michigan is an elevation of 579.6 feet above mean sea level. Depths on the Lake Survey charts referred to standard low water are 1 foot less than those published herein. The depths for Lake Superior herein given are referred to low water datum, the reference plane for United States river and harbor improvements, which for Lake Superior is an elevation of 601.6 feet above mean sea level. Depths on the Lake Survey charts referred to standard low water are 1 foot less than those published herein, but depths on the charts of Agate and Eagle harbors referred to an elevation of 602.82 feet above mean sea level are about 1 foot more. Caution. The mariner proceeding from Montreal to any port on the Great Lakes will use Canadian charts, Hydrographic Office charts, and Lake Survey charts. The distances, bearings, and the compass roses on these charts differ, so the mariner is cautioned to consult the notes on the chart in use to ascertain the scale and bearing. Summary of Notices to Mariners. While it is the intention of the Hydrographic Office to publish about the first of each year a Summary of Notices to Mariners, of the preceding year, affecting the volume, it must be understood that these summaries are intended to include only important changes and corrections, and that their publication may be discontinued at any time, especially when a new edition of the book is issued. Masters of vessels should keep complete files of weekly Notices to Mariners and supply themselves with the latest List of Lights and seek from local authorities, pilots, and harbor masters the latest information relative to any special regulations in force in the particular locality visited. Mariners are requested to notify the United States Hydrographic Office, Washington, D. C., or one of its branch offices, of errors they may discover in this publication, or of additional matter which they think should be inserted. CONTENTS. Page. The depths for Lake Huron herein given are referred to low- water datum, the reference plane for United States river and harbor improvements, which for Lake Huron is an elevation of 579.6 feet above mean sea level. Depths on the Lake Survey charts, referred to standard low water, are generally 1 foot less than those published The data of the soundings for Georgian Bay and North Channel are given at the beginning of each chapter. The depths for Lake Michigan herein given are referred to low water datum, the reference plane for United States river and har- bor improvements which for Lake Michigan is an elevation of 579.6 feet above mean sea level. Depths on the Lake Survey charts referred to standard low water are 1 foot less than those published The depths for Lake Superior herein given are referred to low water datum, the reference plane for United States river and har- bor improvements, which for Lake Superior is an elevation of 601.6 feet above mean sea level. Depths on the Lake Survey charts re- ferred to standard low water are 1 foot less than those published Caution. The mariner proceeding from Montreal to any port on the Great Lakes will use Canadian charts, Hydrographic Office charts, and Lake Survey charts. The distances, bearings, and the compass roses on these charts differ, so the mariner is cautioned to consult the notes on the chart in use to ascertain the scale and Summary of Notices to Mariners.-While it is the intention of the Hydrographic Office to publish about the first of each year a Masters of vessels should keep complete files of weekly Notices to Mariners are requested to notify the United States Hydrographic |