April 6, 1900.] 



SCIENCE. 



537 



that the periods of excessively cold weather 

 here occur less frequently and are much 

 shorter in duration than farther north. 

 The normal annual maximum and mini- 

 mum temperatures are given for the State 

 as 63°F. and 45°F. respectively. As to the 

 question of rainfall and winds, the condi- 

 tions in Maryland may be considered as a 

 general average of those in the eastern 

 United States ; but the rainfall is by no 

 means uniform in different portions of the 

 State, ranging from 31 inches (at one point 

 on the coast) to 53.5 inches at Sunnyside 

 (Garrett county) at an elevation of 2500 

 feet above sea level. 



The relation of Maryland geology to high- 

 way construction is discussed in still greater 

 detail in this same chapter, first as relates 

 to the road bed or foundation, and then as 

 to the character and distribution in the 

 State of road materials. The coastal plain 

 region (which comprises nearly 5000 square 

 miles, or a little more than one-half of the 

 land area of the State) contains mainly un- 

 consolidated deposits of sand, clay and loam. 

 In limited areas however, especially in the 

 western and southern portions of this re- 

 gion, there are found ferruginous gravels 

 (of Potomac, Lafayette or Columbia age) 

 which when properly used are found to have 

 good cementing qualities and make fairly 

 satisfactory road surfaces M'here there is 

 only moderate travel. The marls of this 

 region have not and probably will not be 

 used to any large extent for highway con- 

 struction, for the reason that the beds are 

 seldom indurated and the shell are quickly 

 ground to pieces under the wheels. Even 

 the calcareous members of the eocene, 

 which are indurated and exposed along 

 many of the valleys, when crushed and 

 placed upon the road surfaces, usually grind 

 rapidly under the wheels and do not re- 

 cement with suflBcient strength to bear 

 heavj' and continuous travel. Probably, 

 however, in Maryland as in portions of 



North Carolina and elsewhere, the more 

 silicious of these beds will be found to pos- 

 sess sufficient hardness as well as cement- 

 ing qualities to make excellent roads for 

 light travel. 



Some 250 miles of oj'ster-shell roads 

 have been constructed in the region border- 

 ing the head of Chesapeake Bay, at a cost of 

 from 81000 to $2000 per mile, and the large 

 oyster interests in the bay will doubtless 

 continue to furnish considerable supplies of 

 this material in the future. Possibly this 

 surface would wear better if with the 

 crushed shell were added a moderate ad- 

 mixture of sand or a thin covering of finely 

 crushed stone. In many portions of east- 

 ern Maryland, as indeed over a large por- 

 tion of the entire coastal plain region of 

 the United States, for the improvement of 

 the ordinary roads in the deep sandy re- 

 gions, we shall have to depend upon the 

 proper admixture of clay, and the use of 

 wide tires on draught vehicles to prevent 

 the cutting to pieces of these sand-clay 

 roads during wet weather. 



In central and western Maryland the 

 question of satisfactory materials for road 

 building is much more easily solved, as 

 suitable materials are much more abundant 

 and widely distributed. The character and 

 distribution of these materials are discussed 

 in detail and their distribution is shown on 

 an excellent map of the State on a scale of 

 20 miles to the inch. In the Piedmont 

 plateau region are found trap rocks, includ- 

 ing gabbro and diabase, widely distributed 

 which are valuable for road purposes on ac- 

 count of their excellent wearing and fair 

 cementing qualites. The granitic and 

 quartzitic rocks, of which some possess fair 

 wearing quality, are the most abundant 

 material in this region. The compact lime- 

 stones, which are also widely distributed in 

 this region, have in the past (especially the 

 more siliceous beds) constituted a large 

 portion of the road material used. The ig- 



