90 PROCEEDINGS OF THE ACADEMY OF [March, 



In the "Big Woods," about 6.5 km. (4 miles) southwest of Allen- 

 town, Lehigh County, Pa., the drift covering is thick enough to per- 

 mit the growth of pine trees, and tests have shown the soil acidity 

 of the upland peat to range from subacid down to minimacid. Here 

 were noted the Ericaceae: Pyrola americana, Chimaphila maculata, 

 C. unibellata, Gayhissacia baccata, and Vaccinium stmnineum. In 

 addition Cypripedium acaule and Viola pedata, regarded as acid 

 soil plants, thrive here. 



Some 5 km. (3 miles) northwest of this point is a small knoll 

 formerly occupied by similar woods, but cut over several years ago. 

 The humus has been extensively destroyed, and the soil acids neu- 

 tralized by the underlying limestone, so that the acidity at present 

 is minimacid, but the following Ericaceae have persisted: Azalea 

 nudiflora, Gaylussacia baccata, Vaccinium stamineum, V. vacillans, 

 and V . cory7nbosum. With these are Coynptonia asplenifolia {pere- 

 grina) and Viola pedata, the soil of the last in some cases reaching 

 actual neutrality, a rather unusual occurrence. (This observation 

 was made in early spring; later in the season slight acidity may 

 develop there). 



Similar relations have been observed at some five localities, and are 

 no doubt present at other places through this limestone valley, but 

 nowhere have Ericaceae or other plants usually limited to highly 

 acid soils been found to grow in the neutral to subalkaline soils of 

 the limestone itself. 



Hills in Southeastern Counties of Pennsylvania. 



Describing in this province, as in previous ones, only particularly 

 interesting occurrences, mention may first be made of a contact of 

 sandstone and limestone at Fruitville, Lancaster County. On the 

 sandstone, where the soils range in acidity from mediacid down, 

 Ericaceae such as Azalea nudiflora, Gaylussacia baccata, Vaccinium 

 stamineum, and V. vacillans are abundant. On passing over the 

 contact toward the limestone side, these gradually die out, but two 

 of them, the Gaylussacia and Vaccinium vacillans, extend into lime- 

 stone soil of neutral reaction. It should be noted, however, that 

 these plants are there stunted and obviously not thriving; and they 

 are absent entirely when the soil becomes actually alkaline. 



Thus far acidity data have been given chiefly for sandstone and 

 limestone, so it may be of interest to add what has been observed, 

 in the present region, about other formations. Mica schist and mica 

 gneiss seem to yield normally subacid reactions. Trap rock (diabase) 



