64 THE SAN JUAN RIVER. Book I, 
caused by the combined influence of subterranean drainage 
and of evaporation ; and perhaps the latter alone may be 
sufficient to explain the fact. This lake, with the exception 
of its middle section, is very shallow. While bathing near 
Mateares, I observed that you may walk into it for a great 
distance from the shore, and I was even told at the latter 
place that a man on horseback might cross over to Momo- 
tombito, a distance of twelve or fifteen miles. Whether 
this is true or not I cannot tell, but from my observation 
of the nature of the bottom of the lake I should think it 
very possible. As far as I could observe, the lake rests 
on a horizontal sheet of lava. 
Much has been said respecting the former navigation of 
the San Juan river. Vessels coming directly from Spain, 
it has been stated, have formerly ascended that river, 
passed through the lake of Nicaragua and anchored at 
Granada. Such a thing being now utterly impossible, as 
the reader is aware from my statements in reference to the 
rapids at the Castillo Viejo, a question has been raised as 
to the cause by which the change has been produced. The 
Castillo rapids, it has been maintained, have been purposely 
rendered impassable by the Spaniards throwing rocks into 
the river. This may be true. But, at the same time, 
may not a general diminution of water in the hydrographic 
system of the San Juan river, including the lake of 
Managua, be the principal and original cause of so im- 
portant a change in the natural facilities of communication 
existing in Nicaragua ? I do not know whether these 
considerations have ever been brought to bear on the 
question of the inter-oceanic canal. 
To return to Tipitapa, I have to state that the copious 
hot spring which bursts from the ground on the bank of the 
old river-bed is strongly sulphurous, with excellent medical 
