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Unless one knows to the contrary, he should assume that a ton of finely pulverized limestone is worth more per ton than "agricultural lime." Marl. Marls vary in composition, as limestones do, but there are beds of chalky marl that contain very little clay and sand and are nearly a pure carbonate.
The Cretaceous limestones of Mexico were folded into lofty mountains. A massive range was upfolded where the Wasatch Mountains now are, and various ranges of the Rockies in Colorado and other states were upridged. However slowly these deformations were effected they were no doubt accompanied by world-shaking earthquakes, and it is known that volcanic eruptions took place on a magnificent scale.
"A cannon!" exclaimed the Genoese. "Yes, noble Captain, the gun said to be the largest ever cast." "Didst thou see any of the balls?" "Other carts followed directly loaded with gray limestones chiselled round; and to my inquiry what the stones were for, I was told they were bullets twelve spans in circumference, and that the charge of powder used would cast them a mile."
This is now generally believed to have been the case with the Silurian, Devonian, Carboniferous, Oolitic, and Cretaceous limestones and those nummulitic rocks of tertiary date which bear the closest affinity to the Eozoon reefs of the Lower Laurentian. It has a strike from north-west to south-east, nearly at right angles to the metamorphic strata of the Grampians.
The native villages, exactly resembling those of the Gaboon, are all built near the strip of fine white sand which forms the shore, and upon the sweet water channels which cut deep into the limestones.
During also the deposition of these strata, we have in the intercalated layers of red Pampean-like mud and tosca-rock, and in the passage near S. Juan of the semi-crystalline limestones with agate into tosca undistinguishable from that of the Pampas, evidence of the same action, though continued only at intervals and in a feeble manner.
SUBDIVISIONS AND PHYSICAL GEOGRAPHY. The Devonian is represented in New York and southward by the following five series. We add the rocks of which they are chiefly composed. 5 Chemung . . . . . . sandstones and sandy shales 4 Hamilton . . . . . . shales and sandstones 3 Corniferous . . . . . . limestones 2 Oriskany . . . . . . sandstones 1 Helderberg . . . . . . limestones
I could not see the line of junction of these two limestones, or that of the calcareous formation and the diabasis. The transverse valley which descends from Piedras Negras and the village of San Juan, towards Parapara and the Llanos, is filled with trap-rocks, displaying close affinity with the formation of green slates, which they cover.
But the beginner should be warned not to expect to find evidence of the former sojourn of the sea on all those lands which we are nevertheless sure have been submerged at periods comparatively modern; for notwithstanding the enduring nature of the marks left by littoral action on some rocks, especially limestones, we can by no means detect sea-beaches and inland cliffs everywhere.
The mica in recent volcanic rocks, gabbros, and diorites is usually Biotite, while that so common in metamorphic limestones is usually, if not always, Phlogopite. Amphibole is a general name for all the different varieties of Hornblende, Actinolite, Tremolite, etc., while Pyroxene includes Augite, Diallage, Malacolite, Sahlite, etc.
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