What was the original gospel in 'Buddhism'?

From the Introduction: “In so far as the group of religious ideas called ‘Buddhism’ is conceded to have a history – and I have seen this denied by one or two! – it is generally held, that the earliest known stratum of this group, born in India and thence transplanted to South Asia, came to be known as Hina-yana (the lower ‘vehicle’), otherwise called Theravada (opinion of the elders). Further, that this developed, in Eastern and South-eastern Asia, into what came to be known as Mahayana (the great ‘vehicle’), or further teaching, revealed at first to a chosen few (and by them handed on to a chosen few), coming to be deemed fit for more general presentation in the fullness of time. Not I am not denying that Mahayana presents what may be termed a developed teaching. But I deny that it is a development of Hinayana.”

The book contains the following contents:
1. THE FOUNDER AS INSPRIRED
2. WORDS NEEDED AND WORDS MAKESHIFT
3. DEITY, SOUL, SELF, SPIRIT, IN INDIA
4. DHAMMA AS ,ADATOR
5. OVER-ESTIMATE OF ILL; UNDER-ESTIMATE OF DESIRE
6. THE WAY IN THE WORLDS
7. WHICH WAS THE QUEST?
8. THE AIM; THE GOAL
9. JHANA AS I SEE IT
10. WAYS OF DIVINE LIVING
11. GOTAMA OR BUDDHA?
12. THE MASTER'S SILENCE