Towards the middle of the nineteenth century, the British Government felt it was necessary to demarcate Guyana's borders. In 1840, the British Government in 1840 issued a commission to Robert Schomburgk, a German surveyor, geographer and naturalist, authorizing him to survey and mark out the boundaries of British Guiana. It was the intention of that Government, when the work was completed, to communicate to the Governments of Venezuela and Brazil the views of the British Government as to the true boundary of the colony, and then to settle by negotiation any details to which these Governments might take objection.

In carrying out this commission, Schomburgk personally investigated practically the whole of the country (west of the Essequibo): first, from Barima Point and the Amakura River as far as the confluence of the Acarabisi Creek with the Cuyuni River; later, the whole area stretching west and north between the Essequibo and the Cuyuni.

Schomburgk did not discover or invent any new boundaries. He took particular care to base his reports from actual exploration and information obtained from the Amerindians, as well as from the evidence of Dutch remains at Barima and on the Cuyuni. He, thus, was able determine the limits of Dutch possession and the zone from which all trace of Spanish influence was absent.

With his reports Schomburgk submitted maps of his surveys, on which he indicated the line which he would propose to the British Government for adoption. He also called attention to the fact that the British Government might justly claim the whole basin of the Cuyuni and the Yuruari (a tributary of the Cuyuni located in Venezuela), on the ground that the natural boundary of British Guiana included any territory through which flowed rivers, themselves tributaries of the Essequibo.

With a view of facilitating the negotiations for the adjustment of the boundary, he proposed that Great Britain should consent to surrender its claim to a more extended frontier inland. It was on this principle that he drew the boundary line which since became famous as the Schomburgk Line, which included, therefore, much less territory than that claimed by Great Britain.

It was at this period that the discussions with Venezuela about the boundary commenced. The first approach made by the Venezuelan Government was in January 1841 when, in reply to the British announcement of the boundary, it proposed the negotiation of a Treaty of Limits, and expressed a desire that this Treaty should precede the survey and demarcation of the frontier.

Later in the year, the Venezuelan Government renewed the proposal for the negotiation of a Treaty and, at the same time, protested against Schomburgk's proceedings in placing boundary posts at certain points. The Venezuelan Government was informed, in reply, that in the opinion of the British Government, the negotiation of a Boundary Treaty should follow rather than precede the survey operations. The reply added that although Schomburgk had put up certain marks, he was fully aware that the demarcation as made was merely a preliminary measure open to future discussions between the two Governments. The Venezuelan Ambassador in London, Fortique, renewed his protests, and Lord Aberdeen, then Secretary of State for Foreign Affairs, consented in January 1842 to send instructions for the removal of the boundary posts which had been placed by Schomburgk near the Orinoco. However, at the same time, it was distinctly declared that the British Government was not abandoning any portion of its rights over the territory which was formerly held by the Dutch.

In 1843, Fortique, the Venezuelan Ambassador in London, requested the speedy conclusion of a Treaty to define the boundary between Venezuela and British Guiana. Then in a note of the 31 January 1844, he presented the first formal statement of the Venezuelan claim that the territory of the Republic extended to the Essequibo River.

The main grounds on which this claim was based were the following:

1. Spain was the first discoverer and occupant of the New World.

2. The Spaniards had at an early date explored and occupied the Orinoco and all the contiguous country, and the Barima, Moruka and Pomeroon Rivers.

3. At the time of the Treaty of Munster, the Dutch had no possessions in Guiana, or none at least on the northern and western side of the Essequibo.

4. The Spanish dominion extended as far as the Essequibo, and any possession of the Dutch to the west of that river was an usurpation, and had not been approved by Spain.

The statement concluded by insisting that the Essequibo was the natural boundary between Venezuela and British Guiana, and that the British colonists possessed little or nothing beyond that river.

To this claim a reply was promptly sent by Lord Aberdeen, in which, while it was admitted that the American continent was first discovered and partly occupied by the Spaniards, it was observed that such fact could have no bearing upon the matter under discussion. The reply further pointed out that while Venezuela was without a settlement of any sort upon the territory in question, the concession of the Essequibo as the boundary would involve the immediate surrender by Great Britain of half of British Guiana.

Lord Aberdeen also stated that Great Britain was willing to concede out of friendly regard for Venezuela, a part of the British extreme claim in the upper Cuyuni area, providing that the Amerindian tribes living there should be properly protected.

Lord Aberdeen's proposal, when communicated some time later to the British Guiana Government, was found to be extremely unfavourable to the colony. The British Guiana Government stated that the proposal would interfere with settled districts, and it was characterized by the Governor, Henry Mc Leod, as "going far beyond any concession which the Venezuelans were entitled to expect".

The Venezuelan Government, however, failed to appreciate the large concession of British rights which had been proposed solely as a means of facilitating a satisfactory adjustment of the boundary question. No reply was sent to Lord Aberdeen's Note, and it was consequently decided by the British Government in 1850 that as the proposal had remained for six years and still not accepted, it might be considered as having lapsed. The British Charge d'Affaires in Caracas was instructed to communicate this decision to the Venezuelan Government.

In 1850, the British Government felt that Venezuela was making military preparations aimed at attempting to occupy Barima Point and other territory claimed by Great Britain. There was an immediate exchange of Notes between the two countries, and it was finally agreed that neither party should occupy or encroach upon the territory in dispute, but no definition of the territory was ever discussed.

This arrangement was termed the "Agreement of 1850" to which the Venezuelan Government frequently appealed, but which it repeatedly violated in succeeding years.

Venezuela's first acts of violation were the occupation of fresh positions to the east of its previous settlements, and the founding in 1858 of the town of Nueva Providencia on the right bank of the Yuruari. In consequence of this latter action, the Governor of British Guiana, Philip Wodehouse, was sent in 1858 to Caracas to negotiate for a settlement of the boundary, but he found the Venezuelan State in so disturbed a condition (as a result of civil disturbances) that it was impossible to commence negotiations, and eventually he came away without having effected anything. For the next nineteen years the civil disturbances in Venezuela prevented any resumption of negotiations.