Natural History of District of Coliimhia — McAtee 111 



tials NW, NE, SW and SE printed upon a surface exposed 

 after folding. The vertical rows of squares into which each 

 quarter is divided are designated by letters from A to T 

 and the horizontal rows by numbers from 1 to 23. Indexing 

 to squares is by the familiar method, and capitals exclusively 

 are used. For closer indexing, where desirable, each unit 

 square has the four quarters formed by imaginary lines 

 bisecting the sides, designated (always in lower case), as 



a, b, c, d, thus : - - For instance, Glen Echo is at NW, 



I c I d I 



L 17b ; NW indicating the map quarter, L and 17 the ab- 

 scissae to be followed to their intersection, and b the quad- 

 rant of the square so reached. It should be explained that 

 the lower case letter for close indexing is not used for places 

 actually named on the map. 



In the processes of quartering and ruling the maps slight 

 variations were unavoidable. Indexing was done on a nearly 

 perfect set, however, and in using the index allowance may 

 be made for any notable shifting of the ruling that may be 

 observed on the maps in hand. 



It has been found desirable to group certain items in the 

 index and the following general headings : Building, Fort, 

 Hill, Park, Road, School, and Water, have been adopted to 

 cover all items naturally includible under them. Building 

 includes everything that might be expected, except School, 

 which itself is a complex heading. Exceptions are made in 

 the case of Park, Fort and Hill, when they are compounded 

 into an actual proper name of a place. To illustrate the 

 diversity of inclusions under a single heading, those under 

 Water may be cited : Basin, Bay, Bog, Branch, Brook, Canal, 

 Channel, Creek ^^ Ditch, Falls. Flow, Out, Inlet, Lake, Marsh, 

 Pond, Pool, Race, Reservoir, River, Run, Spring,'^" Swamp, 

 and Water. 



"' In local usage the tidal portion of tributaries of the Potomac below 

 Washington is typically called the creek, while the upper portion is called 

 the run : Thus, Hunting Creek, Cameron Run, Occoquan Crook, Bull Run, 

 Variations in this practice occur, especially near Washington. 



8" The nvimber of springs in tlie area covered by the map is amazing. 

 Over 100 are indexed, and probably this is not more than a tenth of the 

 whole number. 



