Plate XIV. shows Trevithick's route across Costa Rica.
A memorandum in Trevithick's writing, apparently a diary, says:—
"From where we returned our mules to the place where we commenced to make our rafts and boat was eleven days' journey, a distance of 50 or 60 miles. The first and second days after parting with the mules we passed some soft ground, with three or four rivulets of water in narrow vales, about 10 miles on the side of the decline of the high ridge on our left. It could easily be made passable for mules, as the bad places where they could not travel did not exceed two or three miles; and had we kept a little more to the left above the soft ground, probably they could have passed. The next bad place was about a mile after the second pass across the San José River, being a very deep and abrupt vale. Had we never passed the San José River, but left it on our right hand, the road would have been much shorter, and we should have avoided this deep vale, and also the three other vales, and their three rivers of Montelegre, Juan Mora, and Ajerbi. They were, however, small, not more than half the leg in water, which is a proof that their source was not above 10 miles off and must have originated in the side of the high ridge on our left. None of the vales were impassable to mules, except that between the second passing of the river San José and the river Montelegre, which was about a mile, and might be made passable for mules by a diagonal road to be made in the side of the hill a little higher up.
"Only five or six miles of road would require to be made for mules on the whole of the way we came, to where the river Serapique is navigable. We observed that we should have avoided those vales by passing a few miles more to the left, where we saw one continued high ridge running from the highest ridge of the continent, commencing at the volcano and terminating in a point near to where the Serapique River is navigable.
"On a regular decline for perhaps 7000 or 8000 feet in height, down to near sea-level, which would in that distance have given a fall of about half an inch in a yard, four men in ten days would make, I have no doubt, this ridge passable for mules on a regular descent to where the Serapique River is navigable. I have no doubt if we could have spent one week more on our journey we might have passed mules the whole distance with us. To carry machinery from where the Serapique is navigable to the mines is about one-third farther than from the port of Arenas on the south, on which the carriage is two dollars per mule load; three dollars might therefore be charged per mule from the Atlantic side, a much less cost than by way of Matina, or by going around Cape Horn. It would give a speedy communication and a great accommodation to the province of Costa Rica, which I doubt not would gladly contribute to its making.
"The mining district occupies the mountain of Aquacate, nearly equidistant from the port of Punta de Arenas, in the Gulf of Nicoya, and from San José, the capital of the state, about 14 leagues from the former and 12 from the latter. The high road passes through the centre of the district.
"The chief outlay after paying for the mines would be for erecting stamping mills and making railroads."
This broken information barely gives an idea of the importance of the Costa Rica mines, or of what Trevithick did between the time of his landing on the Pacific shore, about 1822, and his leaving the mines on his search for a new route over the Cordillera to the Atlantic shore, about 1826 or 1827. Judging from the rough map on which Trevithick has marked his line of travel across the isthmus, the mines of Machucha, Quebrada-honda, and Coralillo, were inland from the Gulf of Nicoya, on the Pacific, some forty or fifty miles, the latter mine having its water shed into the Rio Grande, while the two other mines, not far off, opened into the Quebrada-honda River. The central high ridge of the Cordillera was between the mines and the Atlantic; indeed the mines are on high ground at the foot of volcanic mountains. San Mateo seems to have been the place of importance near the mines, and probably a well-known mule-track was in use through the mountain ridge to San José, the capital, once numbering thirty thousand inhabitants; but this line failed to reach a good port on the Atlantic coast. The travellers, therefore, abandoned the known track, and turning to the left, made their way between the volcanic peaks of Potos and Barba, hoping that on the eastern slope of the Cordillera navigable rivers would be found either to the Atlantic or to the San Juan de Nicaragua, which joined the Atlantic at the port of San Juan. It was probably at this volcanic ridge that the precipitous road obliged the mules to be sent back. The track was then due north, towards Buona Vista, below which the river Serapique took its rise, running into the river San Juan. Where they crossed this river was fifty or sixty miles from where the mules had left them. Trevithick marked the river-crossing with a steamboat, indicating its navigability; but the writer infers that it had so much of the mountain torrent about it, that the travellers took a line still through unexplored country towards the port of San Juan, on the Atlantic, for the track and the description show that the river San José was crossed, and also another river running to the Atlantic. They probably were stopped by swamps on approaching the San Juan, and retracing their steps to the Serapique, constructed rafts or canoes, and after hairbreadth escapes sailed down it to the junction with the San Juan, and down the latter to its junction with the Atlantic at Port San Juan, or Greytown.
Eleven days were passed from the parting with the mules near the crossing of the highest ground, from whence they saw a continuous ridge, commencing at the volcano and terminating near to where the Serapique is navigable on a regular decline for perhaps seven or eight thousand feet down to near sea-level, giving a fall for the whole distance of about half an inch in a yard, or in railway parlance 1 in 70; for this was what was in Trevithick's head, that his steam-horse should carry where the mule could not, and that miners and machinery should be so taken to his mines from the Atlantic, giving those who chose an opportunity of continuing their railway journey to the Pacific.