84 
HYDEOGEAPHIC EEPOETS. 
direction on one of the three other lines sketched from Tesistepeo below. 
You will therefore get as much knowledge of the country back from the river 
as you can. The difficulty, I fear, in these approaches is not high or mountain- 
ous ground, but wide margins of overflowed lands. 
" You will, in your notes, give the topography of the banks within view or 
access. Note the geological characteristics, the growth, character, and names 
of timber, its value if you can ascertain it, its application to various purposes, 
and availability for commerce. As to your plan, within navigable limits, it 
should be something like the one you have to Mina-titlan, — lengths being 
estimated or measured, and soundings giving greatest depth in channel. As 
the river is not at low water, you cannot tell exactly : and hence may not be 
able to decide the limits of fifteen feet low- water depth— but you can judge of 
the limits of sea navigation pretty nearly. 
"2d. As to the river for shoal-water navigation, you cannot judge as well 
now as if it were lower; but you can survey all the shoals and ascertain of 
what they are composed — observe whether the shoal is due merely to an 
expansion of the stream (in which case it might be deepened by confinement 
and excavation), or whether it is due to a sudden fall over a hard ledge: in 
this latter case the chance of improvement is not so good, particularly at 
extreme low water, for the ledges are natural dams, which make intermediate 
reaches of deep water. Perhaps the sounding-rods I had made would be useful 
to you to judge the character of bottom. 
" If the road should connect with shoal-water navigation, I imagine it will be 
at Suchil, just above the Jaltepec ; for the rapids or rock ledges are above 
that. 
" You might ascend the Jaltepec, if practicable, fifteen or twenty miles, to 
observe the character of a railroad crossing, and the nature of the country on 
its banks." ***** 
Upon your instructions, and upon sundry conversations and 
letters that have passed between us, have been based the opera- 
tions of the hydrographic party, with such results as follow : 
1st. "With regard to determining the proper head of sea naviga- 
tion in the Coatzacoalcos River. The survey of the bar,* made 
by Lieut. "William Leigh, of the U. S. Navy, in January, 1848, 
shows a depth of twelve and a half feet in the shoalest part of 
the channel at extreme low water of spring-tides; and I find 
now on a thorough re-examination, that his chart still remains 
accurate, no changes having occurred since that time. The 
sketch of the riverf from its mouth to Mina-titlan, made during 
* See map number 3 
f Plan number 4. 
