Observation

This question was attempted by few candidates whose performance in the question was poor. An intrusive volcanic activity is the various ways by which molten rocks and gases from below the earth’s crust are forced into cracks and joints within the earth crust where they solidify.  The characteristic features of batholiths are:

• found in areas of volcanic activities
• are very large mass of igneous rocks
• are dome shaped or oval
• are bounded  with steep walls of rock
• usually composed of granite or granodiorite
• form the core of most of the world’s fold mountain ranges
• very extensive 10 – 100 km
• some extend for over hundred kilometres
• continues downwards to enormous depths
• largest and most spectacular of all intrusive landforms
• forms the base on which other intrusive features stand
• may be exposed at the surface after long period of denudation
• may resist erosion and form uplands or inselbergs

e.g.  Chaillu Massif in Gabon; Wicklow Mountains of Ireland, Nyika Granite of Malawi, Cape Coast Batholith in Ghana, Main Range of West Malaysia, Uplands of Brittany in France.

The characteristics of  dykes are:

•  found in areas of volcanic activities
• vertical or slanty rocks across bedding planes
• thickness ranges from few metres to hundreds of metres
• may be several kilometres long
• made of mostly basaltic igneous rocks
• resistant to erosion
• dykes cut across bedding plains
• when exposed across river valleys, they form waterfalls
• may occur in groups called swams
• sides are parallel to each other
• stands as ridge or spur when exposed by agents of denudation
• may be denuded to form long and narrow depressing or shallow trenches.

e.g. the Great dyke of Zimbabwe, Jos Plateau in Nigeria, Cleveland Dyke of Yorkshire in England, Klang Gates Ridge of Kuala Lumpur, Howick Falls on River Mgeni in South Africa.