82 AGKICULTURE. 



delights in exceptional cases, of which he may have met 

 with some, but of which we suspect the great majority to be 

 the products of his own ingenuity, and to be put forward 

 with a view to display the ability with which he could en- 

 counter them. We shall pass by such cases altogether. 

 No doubt they are numerous in the aggregate ; but they 

 form a very small percentage of the work of draining which 

 has to be done or redone in Great Britain. They are, 

 moreover, for the most part too complicated to be quite un- 

 derstood without actual inspection, too varied for useful 

 classification, and must be left to the skill and sagacity of 

 the operator. A slight modification of Johnstone's best and 

 simplest plan, with a few sentences of explanation, will suf- 

 ficiently elucidate Elkiugton's mystery, and will comprehend 

 the case of all simple superficial springs. Perhaps in Agri- 

 cultural Britain no formation is more common than mo- 

 derate elevations of previous material, such as chalk, gravel, 

 and imperfect stone or rock of various kinds, resting upon 

 more horizontal beds of clay or other material less pervious 

 than themselves, and at their inferior edge overlapped by 

 it. For this overlap geological reasons are given, into 

 which we cannot now enter. In order to make our expla- 

 nation simple, we use the words gravel and clay as generic 

 for pervious and impervious material. Our drawing is an 



attempt to combine plan and section, which will probably 

 'be sufficiently illustrative. From A to T is the overlap, 



