60 THE PLANT LIFE OF MARYLAND 



quehanna gravel along the 'Tall-line" belt just alluded to. On the 

 Talbot terrace, in the localities along the Chesapeake where it is 

 widest, Elkton clay and Meadow occur, along with Sassafras loam 

 or Sassafras sandy loam. 



Midland Zone, Lower Midland District. — This district is under- 

 laid by igneous and metamorphic rocks of Archean or early Paleozoic 

 age — granite, gneiss, mica-schist, gabbro, marble and serpentine. The 

 soils are loams and clays conforming with the rocks in distribution 

 and having, in part, chemical as well as physical features of impor- 

 tance to vegetation. The granite, gneiss and mica-schist have given 

 rise to the Cecil loam and the Cecil mica-loam, the slate to Cardiff 

 slate loam, the gabbro to Cecil clay and the serpentine to Conowingo 

 clay. The soil of the most marked chemical character is the Cono- 

 wingo clay. The peculiar vegetation of this soil has long given the 

 areas the name of Serpentine Barrens. Their peculiarity consists in 

 the absence of the greater part of the flora of neighboring soils, the 

 abundance of some plants uncommon elsewhere and the sole occur- 

 rence of at least two species of herbaceous plants. These peculiari- 

 ties of flora are to be ascribed to the toxic effect of the high content 

 of the soil water in magnesium, together with the absence of lime 

 and potash. The Cabbro also presents a few peculiarities of vegeta- 

 tion, chiefly the rarity of several species of Ericaceae and certain 

 forest trees. This may be attributable in part to the high content of 

 the mineral constituents of the soil in magnesium, although the pres- 

 ence of lime makes this somewhat improbable.* The physical char- 

 acter of the soil is a much more obvious cause for the absence of such 

 sand-loving plants as the heaths alluded to. 



Midland Zone, Upper Midland District. — The Upper Midland 

 District possesses a wide diversity of underlying rocks ranging in 

 geological age from Archaean to Triassic, and the soils follow them 

 closely in distribution. No soil surveys have been made in this Dis- 

 trict nor in the Mountain Zone, so their soils are known technically 

 only through surveys made in other states on the same geological 



*The influence of lime in counteracting the toxic effect of magnesium has 

 been shown by May, Bulletin 1, Bureau of Plant Industry. 



