Determination of Formations 9 



except on the sea-coast where new land is constantly 

 being formed in certain places, on the edges of certain 

 lakes where the land is gaining on the water, and to some 

 extent on the talus of cliffs, and on the detritus of 

 mountains. 



The colonisation of waste ground, such as derelict 

 building sites, of ballast heaps, etc., furnish, it is true, 

 very interesting and instructive studies in the succession 

 of plant-communities; but owing to the peculiar nature 

 of the substratum in many of these cases, and also owing 

 to the supply of seed available, these successions do not 

 often lead to the establishment of communities belonging 

 to the normal plant-formations of the country, and such 

 land forms a battle-ground for aliens and casuals. 



In the normal primary development of a formation, as 

 in the retrogressive processes before mentioned, the asso- 

 ciations involved show intimate relations and transitions 

 one to another, and the whole set of associations has 

 a definite flora dependent on the type of soil. It is for 

 these reasons that we consider the entire set of plant- 

 conununities on a given tjrpe of soil, in the same 

 geographical region, and under given climatic conditions, 

 as belonging to one formation, in spite of the diversity of 

 the dominant plant-forms in the different associations. 



The plant-formation thus appears as the whole of the 

 natural and semi-naturaP plant-covering occupying a 

 certain type of soil, characterised by definite plant-com- 

 munities and a definite flora. The "wilder" formations, 

 those less modified by man, for instance sand-dunes, salt- 

 marshes, heaths and moors, are quite easily determined, 

 but where human agency has been extensively at work, 

 a careful study of the flora and vegetation and of their 

 relations to the soil is needed before the formation can be 

 accurately determined. In some cases we cannot as yet 



1 i.e. owing its present form to human activity thongh not planted 

 by man. 



