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130 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
reach firmly established conclusions. In certain cases, however, the topog- 
raphy is so constant in its general features that we feel warranted in 
drawing conclusions. Certain of the lakes of the State of Alagóas, for 
example, afford good examples of lakes produced by coast depression. 
The northernmost of these lakes, the Lagóa do Norte, is surrounded 
on three sides by rather steep-faced Tertiary hills of soft sedimentary 
rocks, The slopes of these hills are of forty-five degrees and in places 
even more. 
I learned from Mr. H. Haynes, Superintendent of the Alagéas Rail- 
way, that a well was driven at the railway shops near the foot of this 
bluff in the city of Maceio to a depth of two hundred metres, — all the 
way in loose materials. The inference is that the steep slope of the 
Tertiary hills continues beneath the surface and that the filled-in sedi- 
ments are more than two hundred metres in thickness. 
Fic. 67. The deep well section at Maceio and its relation to the rocks of 
the hills above the city. 
Where the Alagóas railway runs along the lake shore in some places 
there is barely room for the road-bed between the lake and the hills, 
while at other places broad meadow-like plains or mangrove swamps lie 
between the lake and the hills. At still others the line of the road 
crosses flat-bottomed valleys in passinb from one spur of the hills to 
another. These hills — here steeper and there of gentler slope — extend 
more than three fourths of the way round the lake from Maceio at its 
northeast corner to the east of Coco Seco on the southwest — leaving 
only the ancient mouth of the bay with a flat low border of sand between 
it and the sea. 
The lake is now very shallow, so much so that it is navigable even for 
barcacas (small boats drawing a little more than a metre of water) only 
along one channel on the south side. 
Seen from the lighthouse or from the hills that overlook Maceio, the 
coastal belt inland is mostly one broad flat-topped table-land dropping 
off abruptly on the coast. This table-land is made of sedimentary rocks 
that lie in nearly horizontal beds, laid down during Tertiary times. 
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