What type of meat is used in gyros?

A traditional gyro should be made with at least 50% ground lamb, and the rest beef. The best ground to use is one with a high fat content (this is so that during the remixing it binds and keeps it shape well!). The main flavouring ingredients should always be: garlic, onion, marjoram, rosemary, salt and black pepper. Marjoram and Rosemary are similar to oregano and thyme in flavour (respectively), and are common ingredients in Greek cooking.
Greek gyros recipe
1 pound ground lamb
1/2 cup very finely chopped (or shredded) onion
2 teaspoons fresh minced garlic
3/4 teaspoon sea salt
1/2 teaspoon dried ground marjoram
1/2 teaspoon dried ground rosemary
1/4 teaspoon black pepper

Mix everything together and let sit in the fridge for 1-2 hours.

Blend in a food processor for about 1 minute. (When cooked, this will help give it a more traditional gyro feel on your palate. Otherwise, it just takes like cooked minced meat.)

Form into an oblong around a spit, and slow cook over a grill for around 30-45 minutes, cooking far from the coals, and rotating slowly. Alternatively, bake in the oven in a meatloaf shape for about 45 minutes to 1 hour, at 325 degrees F. It should be a bit dry.

In N.Y. the Gyro cones were comprised of lamb, pork beef or chicken, marinated and made rotisserie style, served with a tzatziki sauce, (yogurt, cukes, garlic, oil red wine vinegar salt sauce)