The paper describes the results of measurement on the variation of reflection co-efficient of the sporadic E echoes and of the statistical study of the variations of amplitude of the same, carried out, over a period of 8 months (March to October, 1952) at the Ionosphere Laboratory of the University of Calcutta. It has been possible from these measurements and studies to discriminate between two types of Es ionisations -thin layer type and ion cloud or blob type-causing the echoes. It was found that there is predominance of different types of ionizations at different hours of day and night. Thus in 78.6% of the cases observed in the early morning hours, the Es ionization was of the cloud or blob type of structure. It is suggested that this type owes its origin to ionization by sporadic meteors which are most frequent in the early morning. During the period of sunrise in the E layer, thin layer type of ionization were found in 83.7% of the cases. Such ionization is probably caused by the production of a sharp ionization density gradient at the bottom of the E layer, due to photo-detachment of electrons from negative ions of 0 and 02 by sun's rays coming from below the horizon. The most common type of Es ionization in the afternoon and evening hours was found to be a mixture of the thin layer and ion cloud types. These owe their origin to travelling ion clouds coming from above. Observations also showed that Es ionization (of the mixed type, with a slight preponderance of the thin layer type) was associated with thunderstorms. Blanketing types of Es are also observed during thunderstorms. Occasionally, some thin layer types of ionizations were also observed in the morning, a few hours after sunrise. The origin of these ionizations seems to be due to some modifications of the E layer structure. © 1953.