Geoff Chapple - Terrain

I t took a while to get used to the geologists small talk. In the course of a year, Id hear a lot of it, but Mike Isaac was the first. Coming down to the Cape Reinga lighthouse, he scuffed the distinctly rutilant gravel path and mused

Red chert. From the McCallum Brothers Quarry on Karamuramu Island in the Hauraki Gulf.

We walked on down to the flat apron surrounding the Cape Reinga lighthouse and he wiped a Teva-sandalled foot across the flagstones.

More geological pollution.

It was a phrase geologists tend to use when some human agency has disguised the original outcrop with imported rock.

Limestone, said Mike, from the Paradise Quarry near Whangarei. Pity its not a better colour. A bit grey-green, a bit cold-looking. If it was a nice warm Cotswold colour this would be a very popular building stone.

Mikes inquisition of the surrounding rocks never stopped. It was an eerie skill, far more than knowing the source quarries and the uses a human economy had impressed upon the stone. The rocks yielded clues of crystal and grain size, of the fractional melt that gives the hardest rocks their character as they come up from the mantle. Mike went across to the rock wall that edged the apron, looked it over and pronounced gabbro, dolerite and basalt boulders, probably trucked in from Larmer Road Quarry at Kaitaia.

You can see the crystals in the gabbro are much bigger. Same chemistry as the basalt, but its cooled a lot slower. The crystals have time to separate out and form.

Such was the chatter at the Cape Reinga light, but Id wanted something else from Mike. I wanted to know about what geologists in their more light-hearted moments call the Great Thon. Slumbering beneath the various lapidary distractions as we came onto the Cape was the Great Thon. Thats why we were here, and even a geological newbie like me could feel its power. The land ended in stunted vegetation and steep cliffs of basalt. This was where, according to their mythology, the Maori dead descended to the underworld. Beyond, the Tasman Sea and the Pacific Ocean creased together and the world turned blue. It was a more elegant entrance than the limestone caves at the tip of the Peloponnese or the volcanic throat beneath Lake Avernus, Italy, the Old World portals. Orpheus the Greek, or Aeneas the Trojan anyone who entered the Old World portals was warned by shrieking goddesses and a noisy chorus of harpies and gorgons how easy it was to go in, how hard to come out. But at Cape Reinga, today at least, there was only a moderate salt wind, and nor did you have to descend through the portals at all. You could get there and get out again, mortality intact, for the underworld had heaved itself ashore and we were standing on it.

I d persuaded Mike to come up to the Cape for two reasons. When mapping out a route for the Te Araroa trail in the 1990s and 2000s, Id had a lot of New Zealand roll away under my boots. The continental variety of that landscape is well known, but Id felt the changes underfoot as a slow and salutary revelation. I wanted to know more. I wanted to start in the north and seek out a longer history of the trails best landscapes. But I was going to need help. I put out feelers to see who might explain the complex geology of Northland, and the word came back: Mike Isaac. I went to his Leigh house. There was a Morgan in the garage, a table of fossils beside the front door, and beer in the fridge. The man who owned the Morgan, who opened the front door and later the beer, was fit and feisty. He was bearded, as many geologists are, but it was a short trimmed beard and hardly softened an incisive face.

By reputation he didnt suffer fools, and by reputation he had an encyclopaedic grasp of New Zealand geology, gleaned both from fieldwork and running the Q-Map project that laid out New Zealands geology at a 1:250,000 scale. He was known as a maverick. There were witnesses to say Mike had been a boulder roller during his scientific stints in Antarctica, prising loose rocks and setting them bounding away for minutes at a time down the enormous runout slopes of the frozen continent, ricocheting off the nunataks, bouncing off the dolerite columns. Within his Leigh house I found ammonites in the bathroom and chalcedony quartz, sliced open and polished to display the growth rings.

In 2011, long before our first meeting at Leigh, Mike Isaac had come to Te Araroas opening ceremony at Island Bay, a memorable Wellington day that began with the full pomp of an army band, and ended with a 5.3 earthquake. He was a walker whod done the Camino de Santiago with his wife Maggie, and regularly walked the bush trails around his Leigh house. These were points of contact.

The Northland Allochthon the Great Thon was finally confirmed in the late 1980s, when a Geological Survey team that included Mike put it beyond doubt. Before that, from the late nineteenth century and for most of the twentieth, Northlands strange mix of rock strata had led geologists to question their field data and to contradict each other. It broke friendships, and it drove at least one of its early geologists to drink. For over 100 years the only description that seemed to fit the Far North was chaos.

All that erosion in a subtropical climate, said Mike. All that rampant vegetation. It took a while for people to see that Northland was like the Swiss Alps.

I n 1848, Arnold Escher, a geologist whose territory included the Glarus Alps in central Switzerland, walked over the Segnas Pass with the greatest geology luminary of that time, Sir Roderick Murchison.

Swiss geology allotted whole cantons to its distinguished scientists and they usually kept it within the family, passing on the jurisdiction and the knowledge father to son. The system was aristocratic, though in the Swiss way it should serve the public good. The social service of Arnolds father, Hans Conrad Escher, included engineering the Linth River to prevent the regular flooding of riverside agricultural land, but he also ventured deeper into the Alps, where geology became pure, and speculative, a goad to the imagination. Once, looking up at Mt Nollen, its upturning strata picked out by snow, Hans Conrad had been assailed by a strong vision of the earths crust in motion, unfolding.

By the time Arnold Escher inherited his fathers bailiwick, European and British geologists, Murchison pre-eminent among them, had developed a system of dating rock strata by index fossils. Arnold Escher had applied the system to the Glarus Alps, and his walk with Murchison was a chance to unburden himself of a vision more unsettling than anything that had happened on Mt Nollen. Folds within Swiss alpine strata were commonplace, including the most extreme form, the so-called recumbent folds that turned stratigraphy on its head. But as they walked, with the relevant strata exposed alongside and literally to hand, Escher showed Murchison where Jurassic rocks that were 200 million years old lay over Eocene and Miocene rocks that were only around 50 million years old. That inversion of the proper order, said Escher, stretched in his own jurisdiction over 10 miles to the Panix Pass, and he believed the inversion ran on, straddling the distance between the Bern and Glarus cantons, a distance of over 100 miles. It didnt look much like a recumbent fold.