2) The Panther Gates at 3rd St., like all the statuary that rings the park, is post Olmsted/Vaux and over their dead bodies, as it were. They didn’t want anything like that in or around their rustic-in-urban park. A nice illustration of how fashion changes; the late 19th C fad for memorials, many for the Civil War, came about a generation after the war, when many of the veterans were on their last legs.

You said “Manhattan schist, part of the solid bedrock support responsible for making skyscrapers possible on Manhattan, formed about 450 million years ago. Back then, it was part of the super continent Pangea. The schist is the second oldest component of New York City’s bedrock, after Fordham Gneiss. The schist became part of Manhattan island during continental collision between the floor of the Atlantic Ocean and the East Coast of North America.”

There are several errors in this paragraph. Here are my tweaks:
The Manhattan schist was metamorphosed 450 million years ago, but metamorphic rock comes from other rock, so the original rock is older than 450 Ma, though we can’t say how much older. The process of subduction that closed the predecessor to the Atlantic Ocean (and made Pangea) began around 450 Ma with a series of smaller scale collisions, but Pangea itself didn’t form until about 300 Ma. If you want the gory details, it goes something like this:
OLDEST Taconian Orogeny ~450 Ma (caused by collision of North America with a chain of volcanic islands, like modern day Indonesia)
MIDDLE Acadian Orogeny ~360 Ma (caused by collision of North America with a micro-continent, like modern-day Madagascar)
MOST RECENT Alleghanian Orogeny ~300 Ma to ~250 Ma (caused by collision of North America with Africa, the leading edge of the southern supercontinent Gondwana)

The name of the ocean basin that closed, bringing these disparate crustal fragments together was not Atlantic but “Iapetus.” (Check the relationship of Iapetus to Atlas in Greek mythology for a neat tie-in.) When the Iapetus died, Pangea was born. When Pangea died (rifted and broke up), only then was the Atlantic born. The oldest oceanic crust in the Atlantic is ~200 Ma (same age as your brownstones), and that’s less than half the age of the metamorphic bedrock of Manhattan.

Another quibble is with your presentation that “Geologist [sic] call the first epoch of Earth’s history the “Precambrian.”” This is not true. Epochs are subdivisions of periods, and periods are subdivisions of eras, which are subdivisions of eons. Informally, the term “Precambrian” is used to refer to all chunks of time prior to the Cambrian period, but it is neither an official term, nor an “epoch” (nor an “era”).

I offer these comments up in hopes of enriching your future explorations of geology. I’m looking forward to reading more of your adventures and explications!