The loud, sudden, crunching, crashing halt to a power mower’s roar — the kind of sound you’d hate to hear when mowing your lawn — and a maiden voyage to the top of a Pioneer Valley landmark are on the front burner of discussion this week.

First, the grinding, earth-rattling sound I heard while walking the dogs Monday morning. I had just turned the corner onto the short second leg of my daily Sunken Meadow ramble. It sounded bad, like the mower attached behind a John Deere tractor had hit an outcropping of hidden, immovable bedrock, bringing the rotating blades to a loud, grinding stop. My first fear was the dogs, but I had heard no tell-tale yelp, so I paused and saw them both rollicking freely faraway from danger. After the tractor had been briefly idled down, I soon heard the mower restart and mowing had resumed before I turned the corner of dense, eight- or 10-foot-high sumacs hanging overhead. The farmhand who, on the side, keeps the Christmas-tree farm tidy, was mowing toward the beaver pond when I spotted him. I knew we were on a collision course and would soon cross paths. When that moment arrived, he stopped, again idled down the tractor, pulled out his earplugs and said, shaking his head in bewilderment, “I just hit another turtle in the tall grass.” Then, pointing north, “It’s in that row right there, back by the split. All I can tell you is it’s big with big claws.”

“Oh, so that’s what I heard?” I answered. “Probably a snapper. I’ll take a look when I get there. It sounded like a rock.”

I continued on my merry way with the dogs, who, at the large riverside apple squeezed down a thin beaver lane to the river and submerged themselves for sloppy drinks before returning back onto the floodplain and continuing on our normal path back toward the truck. At a crossroads 100 feet north, I turned west, walked through another crossroads, identified the fourth mowed lane and walked down it to investigate the carnage. Sure enough, a snapping turtle about a foot wide and a bit longer, overturned with a small hole through it’s under-shell exposing eggs. I poked it with my polished chestnut crook cane and it moved its legs and head. Not sure if it was living or just a twitching bundle of nerves performing its death dance, I flipped it right side up to at least give it what appeared to be a slim chance of walking away. Though the big shelled reptile was in better than expected shape for what it had been through, I figured I would find it dead the next day, perhaps on the spot where I left it.

I was wrong. Twenty-four hours later, that big turtle had vanished, nowhere to be found, and, trust me, they don’t move fast, especially when wounded. No only that, but I don’t know of a predator that could have carried the beast off — too heavy and awkward. My buddy was down there cutting up a fallen beaver tree that’s been protruding out into the Christmas trees for weeks, and he said he hadn’t touched the turtle. So I figured it must have walked off, maybe to die, maybe not. I’d look around and try to keep my dogs away from an ornery snapper, which they would smell long before bumping into it, then proceed with caution. I had no idea if a big snapping turtle with a hole poked through it’s lower shell could survive, but I didn’t doubt it. They sure look like tough prehistoric hombres to me.

But, no, that turtle didn’t make it. My buddy was again out mowing Wednesday morning and, in passing, he stopped, half-grinned wryly and said, “Can you smell it? It’s right there. She didn’t go far.”

Yup, the dogs had already discovered the stench and were rolling in it five feet from where the critter had snugged up to the base of a small Christmas tree and died. It might have walked 20 feet before expiring, no more.

Which brings us to Mt. Tom, a distinctive Pioneer Valley peak I’ve known for most of my life, can identify from afar by its shape but had never before last week climbed to the summit, looking down at the Northampton Oxbow. The closest I had ever come to the summit visited on a rainy, foggy Thursday morning with South Deerfield friend Bud Driver and Mount Holyoke College geology professor Steven Dunn had been boyhood trips to Mountain Park. Dunn was interested in ancient chert, or flint, quarries I had written about a few months back and had contacted Driver — the discoverer who named the stone “Roisin Dalby chert of the Pioneer Valley,” and who had brought various scholars there to collect and analyze samples in 1998. When I shed new light on the subject recently after a minuscule percentage of “bi-face yard” chips collected at a Paleoindian excavation site below Mt. Sugarloaf was identified as local chert, the word got out to the Five-College Consortium through Greenfield Community College geologist Richard Little. That’s when Dunn called Driver to request a tour of the high site overlooking Northampton and Easthampton. Driver agreed, invited me to join them and the rest is history.

We met at the state Department of Conservation and Recreation office on the lower eastern slope of the range, where we met manager Robert Carr before driving to a parking area on a western promontory and walking to large, flat, mountaintop outcropping of reddish-colored ledge Driver dubbed the “Sitting Stone,” where ancient Stone-Age flint-knappers once fashioned tools and left many flakes still to be recovered with minimal digging. Even more interesting to me were the many geometric designs carved into the flat stone. Dunn examined and was intrigued by the lines, stating that many appeared to him to be man- made, definitely not marks carved by sliding glaciers, which typically point southeast. Were we looking at ancient graffiti related to constellations? Who knows? More research is needed, and I know just the man for the job.

Anyway, the Mt. Holyoke scientist gathered many loose chert samples off the steep upper-western slope and brought them back to his college laboratory for careful thin-section analysis. Although he doesn’t question published findings by Connecticut lithics experts Anthony Philpotts and Barbara Calogero, he wanted to confirm that the stone was indeed chert. Such stone was formed in ancient marine environments and should not, in his opinion, exist on Pioneer Valley ranges like Mt. Tom, Mt. Holyoke and Pocumtuck.

I’ve said it before and will again state that what makes this subject and many related offshoots so interesting is what little really is known. Yes, there are many heady hypotheses, but just when the experts feel confident they have one pinned down — Whammo! — along comes a new discovery to roil a clear liquid into cloudy uncertainty.