4a SURFACE OF jTHE EARTH. nedion^ard either.ifpkled, orfeyeral are joined to- gether^ihrming^a .of mountain groups. ’i< :: .... ..vjt’It 25. Plains, as we have already mentioned, form 'PW<pipa^, copftituent part of low landj yet there frequently occurs in it flat hilly land, and mpre .rarely ; Iqw and s ifalated mountain groups; and the mountains are often ifolated, and at a con- fiderable diftance from each other. The plains of the low land are chara&erifed by particular hollows, or concavities, which are deno minated river valleys, or river courfes. In thefe there are to be diftinguifhed the bed of the river, and the bolm pr haugb land : Further, there are to be ob- ferved the bigb,and low bank of the river, and the ravines or fmall valleys that traverfe the high bank, and terminate in the low bank. There is ftill another ,kind of hollow to be ob- ferved in low land; it is that formed by lliallow and wide-extended lakes. Numerous inftances of this are to be obferved in the great European low land. The Marc Brandenburg affords many in ftances of thefe latter. We further obferve, that the plains of the low land arc not perfedly level but are frequently marked with riling grounds’ Which can fcarcely be entitled to the name of hills’ They often extend for many miles. They are de nominated by German geognofts Landhbhen, when they are nearly of equal length and breadth ; and Lctndrucken, when they have a lengthened form. 26. In
